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From: "jsm28 at gcc dot gnu.org" <sourceware-bugzilla@sourceware.org> To: glibc-bugs@sourceware.org Subject: [Bug stdio/26211] New: printf integer overflow calculating allocation size Date: Mon, 06 Jul 2020 23:03:36 +0000 [thread overview] Message-ID: <bug-26211-131@http.sourceware.org/bugzilla/> (raw) https://sourceware.org/bugzilla/show_bug.cgi?id=26211 Bug ID: 26211 Summary: printf integer overflow calculating allocation size Product: glibc Version: 2.32 Status: NEW Severity: normal Priority: P2 Component: stdio Assignee: unassigned at sourceware dot org Reporter: jsm28 at gcc dot gnu.org Target Milestone: --- The following test segfaults on a 64-bit system (haven't tested 32-bit). (Any precision less than 0x7fffffe0 is OK; 0x7fffffe0 through 0x7fffffff result in the crash.) #include <stdio.h> #include <stdlib.h> int main (void) { FILE *fp; if ((fp = fopen ("/dev/null", "w")) == NULL) exit (1); fprintf (fp, "%2$.*1$a", 0x7fffffff, 1e200); } The problem is the code in printf_positional: /* Maybe the buffer is too small. */ if (MAX (prec, width) + EXTSIZ > WORK_BUFFER_SIZE) { if (__libc_use_alloca ((MAX (prec, width) + EXTSIZ) * sizeof (CHAR_T))) workend = ((CHAR_T *) alloca ((MAX (prec, width) + EXTSIZ) * sizeof (CHAR_T)) + (MAX (prec, width) + EXTSIZ)); else { workstart = (CHAR_T *) malloc ((MAX (prec, width) + EXTSIZ) * sizeof (CHAR_T)); if (workstart == NULL) { done = -1; goto all_done; } workend = workstart + (MAX (prec, width) + EXTSIZ); } } The code in the implementation that doesn't use '$' argument numbers has a check if (__glibc_unlikely (width >= INT_MAX / sizeof (CHAR_T) - EXTSIZ)) { __set_errno (EOVERFLOW); done = -1; goto all_done; } (and likewise for precision). The implementation for the case with '$' argument numbers is missing that check. So MAX (prec, width) + EXTSIZ overflows. -- You are receiving this mail because: You are on the CC list for the bug.
next reply other threads:[~2020-07-06 23:03 UTC|newest] Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-07-06 23:03 jsm28 at gcc dot gnu.org [this message] 2020-07-07 14:54 ` [Bug stdio/26211] " cvs-commit at gcc dot gnu.org 2020-07-07 14:57 ` jsm28 at gcc dot gnu.org 2022-08-29 15:06 ` cvs-commit at gcc dot gnu.org 2022-08-30 8:23 ` cvs-commit at gcc dot gnu.org 2022-08-30 8:45 ` cvs-commit at gcc dot gnu.org 2022-08-30 8:45 ` cvs-commit at gcc dot gnu.org 2022-08-30 8:48 ` cvs-commit at gcc dot gnu.org 2022-08-30 9:20 ` cvs-commit at gcc dot gnu.org 2022-08-30 9:20 ` cvs-commit at gcc dot gnu.org 2022-08-30 11:07 ` cvs-commit at gcc dot gnu.org 2022-08-30 11:08 ` cvs-commit at gcc dot gnu.org
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