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* [Bug libc/28769] New: Off-by-one buffer overflow/underflow in getcwd() (CVE-2021-3999)
@ 2022-01-12 13:44 siddhesh at sourceware dot org
2022-01-12 13:45 ` [Bug libc/28769] " siddhesh at sourceware dot org
` (9 more replies)
0 siblings, 10 replies; 11+ messages in thread
From: siddhesh at sourceware dot org @ 2022-01-12 13:44 UTC (permalink / raw)
To: glibc-bugs
https://sourceware.org/bugzilla/show_bug.cgi?id=28769
Bug ID: 28769
Summary: Off-by-one buffer overflow/underflow in getcwd()
(CVE-2021-3999)
Product: glibc
Version: 2.35
Status: NEW
Severity: normal
Priority: P2
Component: libc
Assignee: siddhesh at sourceware dot org
Reporter: siddhesh at sourceware dot org
CC: drepper.fsp at gmail dot com
Target Milestone: ---
Flags: security+
For very long file names, the getcwd syscall returns ENAMETOOLONG, resulting in
a call to __getcwd_generic. That function in turn assumes a size that's
suficient for at least a '/', so a size of 1 results in access that's one byte
beyond bounds of buf.
We always need a minimum size of 2 bytes, so the glibc function should set
ERANGE and return NULL for size of 1 byte.
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* [Bug libc/28769] Off-by-one buffer overflow/underflow in getcwd() (CVE-2021-3999)
2022-01-12 13:44 [Bug libc/28769] New: Off-by-one buffer overflow/underflow in getcwd() (CVE-2021-3999) siddhesh at sourceware dot org
@ 2022-01-12 13:45 ` siddhesh at sourceware dot org
2022-01-12 13:48 ` fweimer at redhat dot com
` (8 subsequent siblings)
9 siblings, 0 replies; 11+ messages in thread
From: siddhesh at sourceware dot org @ 2022-01-12 13:45 UTC (permalink / raw)
To: glibc-bugs
https://sourceware.org/bugzilla/show_bug.cgi?id=28769
Siddhesh Poyarekar <siddhesh at sourceware dot org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |ASSIGNED
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* [Bug libc/28769] Off-by-one buffer overflow/underflow in getcwd() (CVE-2021-3999)
2022-01-12 13:44 [Bug libc/28769] New: Off-by-one buffer overflow/underflow in getcwd() (CVE-2021-3999) siddhesh at sourceware dot org
2022-01-12 13:45 ` [Bug libc/28769] " siddhesh at sourceware dot org
@ 2022-01-12 13:48 ` fweimer at redhat dot com
2022-01-12 13:48 ` fweimer at redhat dot com
` (7 subsequent siblings)
9 siblings, 0 replies; 11+ messages in thread
From: fweimer at redhat dot com @ 2022-01-12 13:48 UTC (permalink / raw)
To: glibc-bugs
https://sourceware.org/bugzilla/show_bug.cgi?id=28769
Florian Weimer <fweimer at redhat dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |fweimer at redhat dot com
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* [Bug libc/28769] Off-by-one buffer overflow/underflow in getcwd() (CVE-2021-3999)
2022-01-12 13:44 [Bug libc/28769] New: Off-by-one buffer overflow/underflow in getcwd() (CVE-2021-3999) siddhesh at sourceware dot org
2022-01-12 13:45 ` [Bug libc/28769] " siddhesh at sourceware dot org
2022-01-12 13:48 ` fweimer at redhat dot com
@ 2022-01-12 13:48 ` fweimer at redhat dot com
2022-01-15 15:41 ` aurelien at aurel32 dot net
` (6 subsequent siblings)
9 siblings, 0 replies; 11+ messages in thread
From: fweimer at redhat dot com @ 2022-01-12 13:48 UTC (permalink / raw)
To: glibc-bugs
https://sourceware.org/bugzilla/show_bug.cgi?id=28769
Florian Weimer <fweimer at redhat dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
See Also| |https://bugzilla.redhat.com
| |/show_bug.cgi?id=2024637
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* [Bug libc/28769] Off-by-one buffer overflow/underflow in getcwd() (CVE-2021-3999)
2022-01-12 13:44 [Bug libc/28769] New: Off-by-one buffer overflow/underflow in getcwd() (CVE-2021-3999) siddhesh at sourceware dot org
` (2 preceding siblings ...)
2022-01-12 13:48 ` fweimer at redhat dot com
@ 2022-01-15 15:41 ` aurelien at aurel32 dot net
2022-01-17 9:07 ` pgowda.cve at gmail dot com
` (5 subsequent siblings)
9 siblings, 0 replies; 11+ messages in thread
From: aurelien at aurel32 dot net @ 2022-01-15 15:41 UTC (permalink / raw)
To: glibc-bugs
https://sourceware.org/bugzilla/show_bug.cgi?id=28769
Aurelien Jarno <aurelien at aurel32 dot net> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |aurelien at aurel32 dot net
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* [Bug libc/28769] Off-by-one buffer overflow/underflow in getcwd() (CVE-2021-3999)
2022-01-12 13:44 [Bug libc/28769] New: Off-by-one buffer overflow/underflow in getcwd() (CVE-2021-3999) siddhesh at sourceware dot org
` (3 preceding siblings ...)
2022-01-15 15:41 ` aurelien at aurel32 dot net
@ 2022-01-17 9:07 ` pgowda.cve at gmail dot com
2022-01-24 6:01 ` cvs-commit at gcc dot gnu.org
` (4 subsequent siblings)
9 siblings, 0 replies; 11+ messages in thread
From: pgowda.cve at gmail dot com @ 2022-01-17 9:07 UTC (permalink / raw)
To: glibc-bugs
https://sourceware.org/bugzilla/show_bug.cgi?id=28769
pgowda <pgowda.cve at gmail dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |pgowda.cve at gmail dot com
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* [Bug libc/28769] Off-by-one buffer overflow/underflow in getcwd() (CVE-2021-3999)
2022-01-12 13:44 [Bug libc/28769] New: Off-by-one buffer overflow/underflow in getcwd() (CVE-2021-3999) siddhesh at sourceware dot org
` (4 preceding siblings ...)
2022-01-17 9:07 ` pgowda.cve at gmail dot com
@ 2022-01-24 6:01 ` cvs-commit at gcc dot gnu.org
2022-01-24 6:46 ` cvs-commit at gcc dot gnu.org
` (3 subsequent siblings)
9 siblings, 0 replies; 11+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2022-01-24 6:01 UTC (permalink / raw)
To: glibc-bugs
https://sourceware.org/bugzilla/show_bug.cgi?id=28769
--- Comment #1 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Siddhesh Poyarekar
<siddhesh@sourceware.org>:
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=23e0e8f5f1fb5ed150253d986ecccdc90c2dcd5e
commit 23e0e8f5f1fb5ed150253d986ecccdc90c2dcd5e
Author: Siddhesh Poyarekar <siddhesh@sourceware.org>
Date: Fri Jan 21 23:32:56 2022 +0530
getcwd: Set errno to ERANGE for size == 1 (CVE-2021-3999)
No valid path returned by getcwd would fit into 1 byte, so reject the
size early and return NULL with errno set to ERANGE. This change is
prompted by CVE-2021-3999, which describes a single byte buffer
underflow and overflow when all of the following conditions are met:
- The buffer size (i.e. the second argument of getcwd) is 1 byte
- The current working directory is too long
- '/' is also mounted on the current working directory
Sequence of events:
- In sysdeps/unix/sysv/linux/getcwd.c, the syscall returns ENAMETOOLONG
because the linux kernel checks for name length before it checks
buffer size
- The code falls back to the generic getcwd in sysdeps/posix
- In the generic func, the buf[0] is set to '\0' on line 250
- this while loop on line 262 is bypassed:
while (!(thisdev == rootdev && thisino == rootino))
since the rootfs (/) is bind mounted onto the directory and the flow
goes on to line 449, where it puts a '/' in the byte before the
buffer.
- Finally on line 458, it moves 2 bytes (the underflowed byte and the
'\0') to the buf[0] and buf[1], resulting in a 1 byte buffer overflow.
- buf is returned on line 469 and errno is not set.
This resolves BZ #28769.
Reviewed-by: Andreas Schwab <schwab@linux-m68k.org>
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Signed-off-by: Qualys Security Advisory <qsa@qualys.com>
Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
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* [Bug libc/28769] Off-by-one buffer overflow/underflow in getcwd() (CVE-2021-3999)
2022-01-12 13:44 [Bug libc/28769] New: Off-by-one buffer overflow/underflow in getcwd() (CVE-2021-3999) siddhesh at sourceware dot org
` (5 preceding siblings ...)
2022-01-24 6:01 ` cvs-commit at gcc dot gnu.org
@ 2022-01-24 6:46 ` cvs-commit at gcc dot gnu.org
2022-01-24 6:47 ` siddhesh at sourceware dot org
` (2 subsequent siblings)
9 siblings, 0 replies; 11+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2022-01-24 6:46 UTC (permalink / raw)
To: glibc-bugs
https://sourceware.org/bugzilla/show_bug.cgi?id=28769
--- Comment #2 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
The release/2.34/master branch has been updated by Siddhesh Poyarekar
<siddhesh@sourceware.org>:
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=472e799a5f2102bc0c3206dbd5a801765fceb39c
commit 472e799a5f2102bc0c3206dbd5a801765fceb39c
Author: Siddhesh Poyarekar <siddhesh@sourceware.org>
Date: Fri Jan 21 23:32:56 2022 +0530
getcwd: Set errno to ERANGE for size == 1 (CVE-2021-3999)
No valid path returned by getcwd would fit into 1 byte, so reject the
size early and return NULL with errno set to ERANGE. This change is
prompted by CVE-2021-3999, which describes a single byte buffer
underflow and overflow when all of the following conditions are met:
- The buffer size (i.e. the second argument of getcwd) is 1 byte
- The current working directory is too long
- '/' is also mounted on the current working directory
Sequence of events:
- In sysdeps/unix/sysv/linux/getcwd.c, the syscall returns ENAMETOOLONG
because the linux kernel checks for name length before it checks
buffer size
- The code falls back to the generic getcwd in sysdeps/posix
- In the generic func, the buf[0] is set to '\0' on line 250
- this while loop on line 262 is bypassed:
while (!(thisdev == rootdev && thisino == rootino))
since the rootfs (/) is bind mounted onto the directory and the flow
goes on to line 449, where it puts a '/' in the byte before the
buffer.
- Finally on line 458, it moves 2 bytes (the underflowed byte and the
'\0') to the buf[0] and buf[1], resulting in a 1 byte buffer overflow.
- buf is returned on line 469 and errno is not set.
This resolves BZ #28769.
Reviewed-by: Andreas Schwab <schwab@linux-m68k.org>
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Signed-off-by: Qualys Security Advisory <qsa@qualys.com>
Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
(cherry picked from commit 23e0e8f5f1fb5ed150253d986ecccdc90c2dcd5e)
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* [Bug libc/28769] Off-by-one buffer overflow/underflow in getcwd() (CVE-2021-3999)
2022-01-12 13:44 [Bug libc/28769] New: Off-by-one buffer overflow/underflow in getcwd() (CVE-2021-3999) siddhesh at sourceware dot org
` (6 preceding siblings ...)
2022-01-24 6:46 ` cvs-commit at gcc dot gnu.org
@ 2022-01-24 6:47 ` siddhesh at sourceware dot org
2022-01-24 22:46 ` cvs-commit at gcc dot gnu.org
2022-01-24 22:49 ` cvs-commit at gcc dot gnu.org
9 siblings, 0 replies; 11+ messages in thread
From: siddhesh at sourceware dot org @ 2022-01-24 6:47 UTC (permalink / raw)
To: glibc-bugs
https://sourceware.org/bugzilla/show_bug.cgi?id=28769
Siddhesh Poyarekar <siddhesh at sourceware dot org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|--- |2.35
Resolution|--- |FIXED
Status|ASSIGNED |RESOLVED
--- Comment #3 from Siddhesh Poyarekar <siddhesh at sourceware dot org> ---
Fixed on trunk and 2.34.
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* [Bug libc/28769] Off-by-one buffer overflow/underflow in getcwd() (CVE-2021-3999)
2022-01-12 13:44 [Bug libc/28769] New: Off-by-one buffer overflow/underflow in getcwd() (CVE-2021-3999) siddhesh at sourceware dot org
` (7 preceding siblings ...)
2022-01-24 6:47 ` siddhesh at sourceware dot org
@ 2022-01-24 22:46 ` cvs-commit at gcc dot gnu.org
2022-01-24 22:49 ` cvs-commit at gcc dot gnu.org
9 siblings, 0 replies; 11+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2022-01-24 22:46 UTC (permalink / raw)
To: glibc-bugs
https://sourceware.org/bugzilla/show_bug.cgi?id=28769
--- Comment #4 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
The release/2.34/master branch has been updated by Aurelien Jarno
<aurel32@sourceware.org>:
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=1b9cd6a7214db1812a20eb3591cf42f9190a5d1a
commit 1b9cd6a7214db1812a20eb3591cf42f9190a5d1a
Author: Aurelien Jarno <aurelien@aurel32.net>
Date: Mon Jan 24 23:45:03 2022 +0100
NEWS: add bug entry for BZ #28769 and BZ #28770
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* [Bug libc/28769] Off-by-one buffer overflow/underflow in getcwd() (CVE-2021-3999)
2022-01-12 13:44 [Bug libc/28769] New: Off-by-one buffer overflow/underflow in getcwd() (CVE-2021-3999) siddhesh at sourceware dot org
` (8 preceding siblings ...)
2022-01-24 22:46 ` cvs-commit at gcc dot gnu.org
@ 2022-01-24 22:49 ` cvs-commit at gcc dot gnu.org
9 siblings, 0 replies; 11+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2022-01-24 22:49 UTC (permalink / raw)
To: glibc-bugs
https://sourceware.org/bugzilla/show_bug.cgi?id=28769
--- Comment #5 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
The release/2.33/master branch has been updated by Aurelien Jarno
<aurel32@sourceware.org>:
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=bcdde07537d733eafe1f28cea3084003e140f5ff
commit bcdde07537d733eafe1f28cea3084003e140f5ff
Author: Siddhesh Poyarekar <siddhesh@sourceware.org>
Date: Fri Jan 21 23:32:56 2022 +0530
getcwd: Set errno to ERANGE for size == 1 (CVE-2021-3999)
No valid path returned by getcwd would fit into 1 byte, so reject the
size early and return NULL with errno set to ERANGE. This change is
prompted by CVE-2021-3999, which describes a single byte buffer
underflow and overflow when all of the following conditions are met:
- The buffer size (i.e. the second argument of getcwd) is 1 byte
- The current working directory is too long
- '/' is also mounted on the current working directory
Sequence of events:
- In sysdeps/unix/sysv/linux/getcwd.c, the syscall returns ENAMETOOLONG
because the linux kernel checks for name length before it checks
buffer size
- The code falls back to the generic getcwd in sysdeps/posix
- In the generic func, the buf[0] is set to '\0' on line 250
- this while loop on line 262 is bypassed:
while (!(thisdev == rootdev && thisino == rootino))
since the rootfs (/) is bind mounted onto the directory and the flow
goes on to line 449, where it puts a '/' in the byte before the
buffer.
- Finally on line 458, it moves 2 bytes (the underflowed byte and the
'\0') to the buf[0] and buf[1], resulting in a 1 byte buffer overflow.
- buf is returned on line 469 and errno is not set.
This resolves BZ #28769.
Reviewed-by: Andreas Schwab <schwab@linux-m68k.org>
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Signed-off-by: Qualys Security Advisory <qsa@qualys.com>
Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
(cherry picked from commit 23e0e8f5f1fb5ed150253d986ecccdc90c2dcd5e)
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2022-01-12 13:44 [Bug libc/28769] New: Off-by-one buffer overflow/underflow in getcwd() (CVE-2021-3999) siddhesh at sourceware dot org
2022-01-12 13:45 ` [Bug libc/28769] " siddhesh at sourceware dot org
2022-01-12 13:48 ` fweimer at redhat dot com
2022-01-12 13:48 ` fweimer at redhat dot com
2022-01-15 15:41 ` aurelien at aurel32 dot net
2022-01-17 9:07 ` pgowda.cve at gmail dot com
2022-01-24 6:01 ` cvs-commit at gcc dot gnu.org
2022-01-24 6:46 ` cvs-commit at gcc dot gnu.org
2022-01-24 6:47 ` siddhesh at sourceware dot org
2022-01-24 22:46 ` cvs-commit at gcc dot gnu.org
2022-01-24 22:49 ` cvs-commit at gcc dot gnu.org
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