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kern/misc: Add sanity check after grub_strtoul() call

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When the format string, fmt0, includes a positional argument
grub_strtoul() or grub_strtoull() is called to extract the argument
position. However, the returned argument position isn't fully validated.
If the format is something like "%0$x" then these functions return
0 which leads to an underflow in the calculation of the args index, curn.
The fix is to add a check to ensure the extracted argument position is
greater than 0 before computing curn. Additionally, replace one
grub_strtoull() with grub_strtoul() and change curn type to make code
more correct.

Fixes: CID 473841

Signed-off-by: Lidong Chen <lidong.chen@oracle.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
This commit is contained in:
Lidong Chen 2025-02-06 18:16:57 +00:00 committed by Daniel Kiper
parent 8e6e87e792
commit a8d6b06331
1 changed files with 7 additions and 2 deletions
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9
grub-core/kern/misc.c
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@ -830,7 +830,7 @@ parse_printf_arg_fmt (const char *fmt0, struct printf_args *args,
while ((c = *fmt++) != 0)
{
int longfmt = 0;
grub_size_t curn;
unsigned long curn;
const char *p;
if (c != '%')
@ -848,7 +848,10 @@ parse_printf_arg_fmt (const char *fmt0, struct printf_args *args,
if (*fmt == '$')
{
curn = grub_strtoull (p, 0, 10) - 1;
curn = grub_strtoul (p, 0, 10);
if (curn == 0)
continue;
curn--;
fmt++;
}
@ -1034,6 +1037,8 @@ grub_vsnprintf_real (char *str, grub_size_t max_len, const char *fmt0,
if (*fmt == '$')
{
if (format1 == 0)
continue;
curn = format1 - 1;
fmt++;
format1 = 0;