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elf: Fix alloca size in _dl_debug_vdprintf

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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>
This commit is contained in:
Szabolcs Nagy 2022-10-11 14:22:35 +01:00
parent 68619ddb3b
commit eef17d4d9f
1 changed files with 5 additions and 2 deletions
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7
elf/dl-printf.c
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@ -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. */