[Bug libc/16060] New: dprintf fails to be async-signal safe

[Bug libc/16060] New: dprintf fails to be async-signal safe

[bugdal at aerifal dot cx]

https://sourceware.org/bugzilla/show_bug.cgi?id=16060

            Bug ID: 16060
           Summary: dprintf fails to be async-signal safe
           Product: glibc
           Version: unspecified
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: libc
          Assignee: unassigned at sourceware dot org
          Reporter: bugdal at aerifal dot cx
                CC: drepper.fsp at gmail dot com

This is NOT a conformance bug, as POSIX does not require dprintf to be AS-safe
or even mention it as an option. However, Roland McGrath has stated on
libc-alpha that, as the original inventor of this interface, he intended it to
be AS-safe and in general not to have unnecessary failure cases. At present,
dprintf fails to be AS-safe for at least the following reasons:

1. It adds and removes the temporary FILE structure it creates to/from the
global open streams list, requiring a lock. This operation is entirely
unnecessary and nonsensical (and also documented in bug #12847).

2. The printf core uses malloc in various places (wide string conversion, i18n
%n$ arguments, ...). Fixing these uses is less trivial, and may not matter to
the most common usage cases for dprintf which are unlikely to hit the code
paths that use malloc, but they are bugs in themselves anyway (unnecessary
failure cases for the entire printf family) which should be fixed.

There may also be other AS-safety issues I am unaware of.

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[Bug libc/16060] dprintf fails to be async-signal safe

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=16060

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
              Flags|                            |security-

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[Bug libc/16060] dprintf fails to be async-signal safe

[f.deldegan at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=16060

Francesco 'pr0gg3d' Del Degan <f.deldegan at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://sourceware.org/bugz
                   |                            |illa/show_bug.cgi?id=12847

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[Bug stdio/16060] dprintf fails to be async-signal safe

[jsm28 at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=16060

Joseph Myers <jsm28 at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|libc                        |stdio

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[Bug stdio/16060] dprintf fails to be async-signal safe

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=16060

--- Comment #1 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Joseph Myers <jsm28@sourceware.org>:

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=6caddd34bd7ffb5ac4f36c8e036eee100c2cc535

commit 6caddd34bd7ffb5ac4f36c8e036eee100c2cc535
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Tue Jul 7 14:54:12 2020 +0000

    Remove most vfprintf width/precision-dependent allocations (bug 14231, bug
26211).

    The vfprintf implementation (used for all printf-family functions)
    contains complicated logic to allocate internal buffers of a size
    depending on the width and precision used for a format, using either
    malloc or alloca depending on that size, and with consequent checks
    for size overflow and allocation failure.

    As noted in bug 26211, the version of that logic used when '$' plus
    argument number formats are in use is missing the overflow checks,
    which can result in segfaults (quite possibly exploitable, I didn't
    try to work that out) when the width or precision is in the range
    0x7fffffe0 through 0x7fffffff (maybe smaller values as well in the
    wprintf case on 32-bit systems, when the multiplication by sizeof
    (CHAR_T) can overflow).

    All that complicated logic in fact appears to be useless.  As far as I
    can tell, there has been no need (outside the floating-point printf
    code, which does its own allocations) for allocations depending on
    width or precision since commit
    3e95f6602b226e0de06aaff686dc47b282d7cc16 ("Remove limitation on size
    of precision for integers", Sun Sep 12 21:23:32 1999 +0000).  Thus,
    this patch removes that logic completely, thereby fixing both problems
    with excessive allocations for large width and precision for
    non-floating-point formats, and the problem with missing overflow
    checks with such allocations.  Note that this does have the
    consequence that width and precision up to INT_MAX are now allowed
    where previously INT_MAX / sizeof (CHAR_T) - EXTSIZ or more would have
    been rejected, so could potentially expose any other overflows where
    the value would previously have been rejected by those removed checks.

    I believe this completely fixes bugs 14231 and 26211.

    Excessive allocations are still possible in the floating-point case
    (bug 21127), as are other integer or buffer overflows (see bug 26201).
    This does not address the cases where a precision larger than INT_MAX
    (embedded in the format string) would be meaningful without printf's
    return value overflowing (when it's used with a string format, or %g
    without the '#' flag, so the actual output will be much smaller), as
    mentioned in bug 17829 comment 8; using size_t internally for
    precision to handle that case would be complicated by struct
    printf_info being a public ABI.  Nor does it address the matter of an
    INT_MIN width being negated (bug 17829 comment 7; the same logic
    appears a second time in the file as well, in the form of multiplying
    by -1).  There may be other sources of memory allocations with malloc
    in printf functions as well (bug 24988, bug 16060).  From inspection,
    I think there are also integer overflows in two copies of "if ((width
    -= len) < 0)" logic (where width is int, len is size_t and a very long
    string could result in spurious padding being output on a 32-bit
    system before printf overflows the count of output characters).

    Tested for x86-64 and x86.

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[Bug stdio/16060] dprintf fails to be async-signal safe

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=16060

--- Comment #2 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
The release/2.31/master branch has been updated by Florian Weimer
<fw@sourceware.org>:

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=1dbe841a672f5d6fdaf73c5d50774a2944a7d42b

commit 1dbe841a672f5d6fdaf73c5d50774a2944a7d42b
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Tue Jul 7 14:54:12 2020 +0000

    Remove most vfprintf width/precision-dependent allocations (bug 14231, bug
26211).

    The vfprintf implementation (used for all printf-family functions)
    contains complicated logic to allocate internal buffers of a size
    depending on the width and precision used for a format, using either
    malloc or alloca depending on that size, and with consequent checks
    for size overflow and allocation failure.

    As noted in bug 26211, the version of that logic used when '$' plus
    argument number formats are in use is missing the overflow checks,
    which can result in segfaults (quite possibly exploitable, I didn't
    try to work that out) when the width or precision is in the range
    0x7fffffe0 through 0x7fffffff (maybe smaller values as well in the
    wprintf case on 32-bit systems, when the multiplication by sizeof
    (CHAR_T) can overflow).

    All that complicated logic in fact appears to be useless.  As far as I
    can tell, there has been no need (outside the floating-point printf
    code, which does its own allocations) for allocations depending on
    width or precision since commit
    3e95f6602b226e0de06aaff686dc47b282d7cc16 ("Remove limitation on size
    of precision for integers", Sun Sep 12 21:23:32 1999 +0000).  Thus,
    this patch removes that logic completely, thereby fixing both problems
    with excessive allocations for large width and precision for
    non-floating-point formats, and the problem with missing overflow
    checks with such allocations.  Note that this does have the
    consequence that width and precision up to INT_MAX are now allowed
    where previously INT_MAX / sizeof (CHAR_T) - EXTSIZ or more would have
    been rejected, so could potentially expose any other overflows where
    the value would previously have been rejected by those removed checks.

    I believe this completely fixes bugs 14231 and 26211.

    Excessive allocations are still possible in the floating-point case
    (bug 21127), as are other integer or buffer overflows (see bug 26201).
    This does not address the cases where a precision larger than INT_MAX
    (embedded in the format string) would be meaningful without printf's
    return value overflowing (when it's used with a string format, or %g
    without the '#' flag, so the actual output will be much smaller), as
    mentioned in bug 17829 comment 8; using size_t internally for
    precision to handle that case would be complicated by struct
    printf_info being a public ABI.  Nor does it address the matter of an
    INT_MIN width being negated (bug 17829 comment 7; the same logic
    appears a second time in the file as well, in the form of multiplying
    by -1).  There may be other sources of memory allocations with malloc
    in printf functions as well (bug 24988, bug 16060).  From inspection,
    I think there are also integer overflows in two copies of "if ((width
    -= len) < 0)" logic (where width is int, len is size_t and a very long
    string could result in spurious padding being output on a 32-bit
    system before printf overflows the count of output characters).

    Tested for x86-64 and x86.

    (cherry picked from commit 6caddd34bd7ffb5ac4f36c8e036eee100c2cc535)

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[Bug stdio/16060] dprintf fails to be async-signal safe

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=16060

--- Comment #3 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
The release/2.30/master branch has been updated by Florian Weimer
<fw@sourceware.org>:

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=2c2357eedebcd93be932031f567c0c66c664131d

commit 2c2357eedebcd93be932031f567c0c66c664131d
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Tue Jul 7 14:54:12 2020 +0000

    Remove most vfprintf width/precision-dependent allocations (bug 14231, bug
26211).

    The vfprintf implementation (used for all printf-family functions)
    contains complicated logic to allocate internal buffers of a size
    depending on the width and precision used for a format, using either
    malloc or alloca depending on that size, and with consequent checks
    for size overflow and allocation failure.

    As noted in bug 26211, the version of that logic used when '$' plus
    argument number formats are in use is missing the overflow checks,
    which can result in segfaults (quite possibly exploitable, I didn't
    try to work that out) when the width or precision is in the range
    0x7fffffe0 through 0x7fffffff (maybe smaller values as well in the
    wprintf case on 32-bit systems, when the multiplication by sizeof
    (CHAR_T) can overflow).

    All that complicated logic in fact appears to be useless.  As far as I
    can tell, there has been no need (outside the floating-point printf
    code, which does its own allocations) for allocations depending on
    width or precision since commit
    3e95f6602b226e0de06aaff686dc47b282d7cc16 ("Remove limitation on size
    of precision for integers", Sun Sep 12 21:23:32 1999 +0000).  Thus,
    this patch removes that logic completely, thereby fixing both problems
    with excessive allocations for large width and precision for
    non-floating-point formats, and the problem with missing overflow
    checks with such allocations.  Note that this does have the
    consequence that width and precision up to INT_MAX are now allowed
    where previously INT_MAX / sizeof (CHAR_T) - EXTSIZ or more would have
    been rejected, so could potentially expose any other overflows where
    the value would previously have been rejected by those removed checks.

    I believe this completely fixes bugs 14231 and 26211.

    Excessive allocations are still possible in the floating-point case
    (bug 21127), as are other integer or buffer overflows (see bug 26201).
    This does not address the cases where a precision larger than INT_MAX
    (embedded in the format string) would be meaningful without printf's
    return value overflowing (when it's used with a string format, or %g
    without the '#' flag, so the actual output will be much smaller), as
    mentioned in bug 17829 comment 8; using size_t internally for
    precision to handle that case would be complicated by struct
    printf_info being a public ABI.  Nor does it address the matter of an
    INT_MIN width being negated (bug 17829 comment 7; the same logic
    appears a second time in the file as well, in the form of multiplying
    by -1).  There may be other sources of memory allocations with malloc
    in printf functions as well (bug 24988, bug 16060).  From inspection,
    I think there are also integer overflows in two copies of "if ((width
    -= len) < 0)" logic (where width is int, len is size_t and a very long
    string could result in spurious padding being output on a 32-bit
    system before printf overflows the count of output characters).

    Tested for x86-64 and x86.

    (cherry picked from commit 6caddd34bd7ffb5ac4f36c8e036eee100c2cc535)

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[Bug stdio/16060] dprintf fails to be async-signal safe

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=16060

--- Comment #4 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
The release/2.29/master branch has been updated by Florian Weimer
<fw@sourceware.org>:

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=5b5dd5a43d0e13529a86332a5c10bdd5b5185e38

commit 5b5dd5a43d0e13529a86332a5c10bdd5b5185e38
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Tue Jul 7 14:54:12 2020 +0000

    Remove most vfprintf width/precision-dependent allocations (bug 14231, bug
26211).

    The vfprintf implementation (used for all printf-family functions)
    contains complicated logic to allocate internal buffers of a size
    depending on the width and precision used for a format, using either
    malloc or alloca depending on that size, and with consequent checks
    for size overflow and allocation failure.

    As noted in bug 26211, the version of that logic used when '$' plus
    argument number formats are in use is missing the overflow checks,
    which can result in segfaults (quite possibly exploitable, I didn't
    try to work that out) when the width or precision is in the range
    0x7fffffe0 through 0x7fffffff (maybe smaller values as well in the
    wprintf case on 32-bit systems, when the multiplication by sizeof
    (CHAR_T) can overflow).

    All that complicated logic in fact appears to be useless.  As far as I
    can tell, there has been no need (outside the floating-point printf
    code, which does its own allocations) for allocations depending on
    width or precision since commit
    3e95f6602b226e0de06aaff686dc47b282d7cc16 ("Remove limitation on size
    of precision for integers", Sun Sep 12 21:23:32 1999 +0000).  Thus,
    this patch removes that logic completely, thereby fixing both problems
    with excessive allocations for large width and precision for
    non-floating-point formats, and the problem with missing overflow
    checks with such allocations.  Note that this does have the
    consequence that width and precision up to INT_MAX are now allowed
    where previously INT_MAX / sizeof (CHAR_T) - EXTSIZ or more would have
    been rejected, so could potentially expose any other overflows where
    the value would previously have been rejected by those removed checks.

    I believe this completely fixes bugs 14231 and 26211.

    Excessive allocations are still possible in the floating-point case
    (bug 21127), as are other integer or buffer overflows (see bug 26201).
    This does not address the cases where a precision larger than INT_MAX
    (embedded in the format string) would be meaningful without printf's
    return value overflowing (when it's used with a string format, or %g
    without the '#' flag, so the actual output will be much smaller), as
    mentioned in bug 17829 comment 8; using size_t internally for
    precision to handle that case would be complicated by struct
    printf_info being a public ABI.  Nor does it address the matter of an
    INT_MIN width being negated (bug 17829 comment 7; the same logic
    appears a second time in the file as well, in the form of multiplying
    by -1).  There may be other sources of memory allocations with malloc
    in printf functions as well (bug 24988, bug 16060).  From inspection,
    I think there are also integer overflows in two copies of "if ((width
    -= len) < 0)" logic (where width is int, len is size_t and a very long
    string could result in spurious padding being output on a 32-bit
    system before printf overflows the count of output characters).

    Tested for x86-64 and x86.

    (cherry picked from commit 6caddd34bd7ffb5ac4f36c8e036eee100c2cc535)

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[Bug stdio/16060] dprintf fails to be async-signal safe

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=16060

--- Comment #5 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
The release/2.28/master branch has been updated by Florian Weimer
<fw@sourceware.org>:

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=e1c0c00cc2bdd147bfcf362ada1443bee90465ec

commit e1c0c00cc2bdd147bfcf362ada1443bee90465ec
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Tue Jul 7 14:54:12 2020 +0000

    Remove most vfprintf width/precision-dependent allocations (bug 14231, bug
26211).

    The vfprintf implementation (used for all printf-family functions)
    contains complicated logic to allocate internal buffers of a size
    depending on the width and precision used for a format, using either
    malloc or alloca depending on that size, and with consequent checks
    for size overflow and allocation failure.

    As noted in bug 26211, the version of that logic used when '$' plus
    argument number formats are in use is missing the overflow checks,
    which can result in segfaults (quite possibly exploitable, I didn't
    try to work that out) when the width or precision is in the range
    0x7fffffe0 through 0x7fffffff (maybe smaller values as well in the
    wprintf case on 32-bit systems, when the multiplication by sizeof
    (CHAR_T) can overflow).

    All that complicated logic in fact appears to be useless.  As far as I
    can tell, there has been no need (outside the floating-point printf
    code, which does its own allocations) for allocations depending on
    width or precision since commit
    3e95f6602b226e0de06aaff686dc47b282d7cc16 ("Remove limitation on size
    of precision for integers", Sun Sep 12 21:23:32 1999 +0000).  Thus,
    this patch removes that logic completely, thereby fixing both problems
    with excessive allocations for large width and precision for
    non-floating-point formats, and the problem with missing overflow
    checks with such allocations.  Note that this does have the
    consequence that width and precision up to INT_MAX are now allowed
    where previously INT_MAX / sizeof (CHAR_T) - EXTSIZ or more would have
    been rejected, so could potentially expose any other overflows where
    the value would previously have been rejected by those removed checks.

    I believe this completely fixes bugs 14231 and 26211.

    Excessive allocations are still possible in the floating-point case
    (bug 21127), as are other integer or buffer overflows (see bug 26201).
    This does not address the cases where a precision larger than INT_MAX
    (embedded in the format string) would be meaningful without printf's
    return value overflowing (when it's used with a string format, or %g
    without the '#' flag, so the actual output will be much smaller), as
    mentioned in bug 17829 comment 8; using size_t internally for
    precision to handle that case would be complicated by struct
    printf_info being a public ABI.  Nor does it address the matter of an
    INT_MIN width being negated (bug 17829 comment 7; the same logic
    appears a second time in the file as well, in the form of multiplying
    by -1).  There may be other sources of memory allocations with malloc
    in printf functions as well (bug 24988, bug 16060).  From inspection,
    I think there are also integer overflows in two copies of "if ((width
    -= len) < 0)" logic (where width is int, len is size_t and a very long
    string could result in spurious padding being output on a 32-bit
    system before printf overflows the count of output characters).

    Tested for x86-64 and x86.

    (cherry picked from commit 6caddd34bd7ffb5ac4f36c8e036eee100c2cc535)

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