[glibc] elf: Fix alloca size in _dl_debug_vdprintf

[glibc] elf: Fix alloca size in _dl_debug_vdprintf

[Szabolcs Nagy]

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.  */