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From: Szabolcs Nagy <nsz@sourceware.org> To: glibc-cvs@sourceware.org Subject: [glibc] elf: Fix alloca size in _dl_debug_vdprintf Date: Fri, 28 Oct 2022 10:18:42 +0000 (GMT) [thread overview] Message-ID: <20221028101842.E693D3857838@sourceware.org> (raw) https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=eef17d4d9fcd38c5cbb9bc9515ba72d1773b67a2 commit eef17d4d9fcd38c5cbb9bc9515ba72d1773b67a2 Author: Szabolcs Nagy <szabolcs.nagy@arm.com> Date: Tue Oct 11 14:22:35 2022 +0100 elf: Fix alloca size in _dl_debug_vdprintf The alloca size did not consider the optional width parameter for padding which could cause buffer underflow. The width is currently used e.g. by _dl_map_object_from_fd which passes 2 * sizeof(void *) which can be larger than the alloca buffer size on targets where sizeof(void *) >= 2 * sizeof(unsigned long). Even if large width is not used on existing targets it is better to fix the formatting code to avoid surprises. Reviewed-by: Florian Weimer <fweimer@redhat.com> Diff: --- elf/dl-printf.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/elf/dl-printf.c b/elf/dl-printf.c index 429d2e80c2..00c114002c 100644 --- a/elf/dl-printf.c +++ b/elf/dl-printf.c @@ -163,8 +163,11 @@ _dl_debug_vdprintf (int fd, int tag_p, const char *fmt, va_list arg) /* We use alloca() to allocate the buffer with the most pessimistic guess for the size. Using alloca() allows having more than one integer formatting in a call. */ - char *buf = (char *) alloca (1 + 3 * sizeof (unsigned long int)); - char *endp = &buf[1 + 3 * sizeof (unsigned long int)]; + int size = 1 + 3 * sizeof (unsigned long int); + if (width + 1 > size) + size = width + 1; + char *buf = (char *) alloca (size); + char *endp = &buf[size]; char *cp = _itoa (num, endp, *fmt == 'x' ? 16 : 10, 0); /* Pad to the width the user specified. */
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