* [PATCH] vfprintf-internal: Get rid of alloca.
@ 2023-05-17 21:28 Joe Simmons-Talbott
2023-05-18 14:08 ` Carlos O'Donell
0 siblings, 1 reply; 2+ messages in thread
From: Joe Simmons-Talbott @ 2023-05-17 21:28 UTC (permalink / raw)
To: libc-alpha; +Cc: Joe Simmons-Talbott
Avoid potential stack overflow from unbounded alloca. Use the existing
scratch_buffer instead.
---
stdio-common/vfprintf-internal.c | 22 +++++++++++++++++++++-
1 file changed, 21 insertions(+), 1 deletion(-)
diff --git a/stdio-common/vfprintf-internal.c b/stdio-common/vfprintf-internal.c
index c76c06e49b..baaefb763a 100644
--- a/stdio-common/vfprintf-internal.c
+++ b/stdio-common/vfprintf-internal.c
@@ -1066,6 +1066,8 @@ printf_positional (struct Xprintf_buffer * buf, const CHAR_T *format,
union printf_arg *args_value;
int *args_size;
int *args_type;
+ int *args_pa_user;
+ size_t args_pa_user_offset;
{
/* Calculate total size needed to represent a single argument
across all three argument-related arrays. */
@@ -1082,6 +1084,7 @@ printf_positional (struct Xprintf_buffer * buf, const CHAR_T *format,
now. */
args_size = &args_value[nargs].pa_int;
args_type = &args_size[nargs];
+ args_pa_user = &args_type[nargs];
memset (args_type, (mode_flags & PRINTF_FORTIFY) != 0 ? '\xff' : '\0',
nargs * sizeof (*args_type));
}
@@ -1171,7 +1174,24 @@ printf_positional (struct Xprintf_buffer * buf, const CHAR_T *format,
else if (__glibc_unlikely (__printf_va_arg_table != NULL)
&& __printf_va_arg_table[args_type[cnt] - PA_LAST] != NULL)
{
- args_value[cnt].pa_user = alloca (args_size[cnt]);
+ if (args_pa_user > argsbuf + args_size)
+ {
+ args_pa_user_offset = args_pa_user - &args_type[nargs];
+ if (!scratch_buffer_grow_preserve (&argsbuf))
+ {
+ Xprintf_buffer_mark_failed (buf);
+ goto all_done;
+ }
+ args_value = argsbuf.data;
+ /* Set up the remaining two arrays to each point past the end of
+ the prior array, since space for all three has been allocated
+ now. */
+ args_size = &args_value[nargs].pa_int;
+ args_type = &args_size[nargs];
+ args_pa_user = &args_type[nargs] + args_pa_user_offset;
+ }
+ args_value[cnt].pa_user = args_pa_user;
+ args_pa_user += args_size[cnt];
(*__printf_va_arg_table[args_type[cnt] - PA_LAST])
(args_value[cnt].pa_user, ap_savep);
}
--
2.39.2
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: [PATCH] vfprintf-internal: Get rid of alloca.
2023-05-17 21:28 [PATCH] vfprintf-internal: Get rid of alloca Joe Simmons-Talbott
@ 2023-05-18 14:08 ` Carlos O'Donell
0 siblings, 0 replies; 2+ messages in thread
From: Carlos O'Donell @ 2023-05-18 14:08 UTC (permalink / raw)
To: Joe Simmons-Talbott, libc-alpha
On 5/17/23 17:28, Joe Simmons-Talbott via Libc-alpha wrote:
> Avoid potential stack overflow from unbounded alloca. Use the existing
> scratch_buffer instead.
Fails 32-bit i686 CI:
https://patchwork.sourceware.org/project/glibc/patch/20230517212847.1821277-1-josimmon@redhat.com/
Please have a look.
> ---
> stdio-common/vfprintf-internal.c | 22 +++++++++++++++++++++-
> 1 file changed, 21 insertions(+), 1 deletion(-)
>
> diff --git a/stdio-common/vfprintf-internal.c b/stdio-common/vfprintf-internal.c
> index c76c06e49b..baaefb763a 100644
> --- a/stdio-common/vfprintf-internal.c
> +++ b/stdio-common/vfprintf-internal.c
> @@ -1066,6 +1066,8 @@ printf_positional (struct Xprintf_buffer * buf, const CHAR_T *format,
> union printf_arg *args_value;
> int *args_size;
> int *args_type;
> + int *args_pa_user;
> + size_t args_pa_user_offset;
> {
> /* Calculate total size needed to represent a single argument
> across all three argument-related arrays. */
> @@ -1082,6 +1084,7 @@ printf_positional (struct Xprintf_buffer * buf, const CHAR_T *format,
> now. */
> args_size = &args_value[nargs].pa_int;
> args_type = &args_size[nargs];
> + args_pa_user = &args_type[nargs];
> memset (args_type, (mode_flags & PRINTF_FORTIFY) != 0 ? '\xff' : '\0',
> nargs * sizeof (*args_type));
> }
> @@ -1171,7 +1174,24 @@ printf_positional (struct Xprintf_buffer * buf, const CHAR_T *format,
> else if (__glibc_unlikely (__printf_va_arg_table != NULL)
> && __printf_va_arg_table[args_type[cnt] - PA_LAST] != NULL)
> {
> - args_value[cnt].pa_user = alloca (args_size[cnt]);
> + if (args_pa_user > argsbuf + args_size)
> + {
> + args_pa_user_offset = args_pa_user - &args_type[nargs];
> + if (!scratch_buffer_grow_preserve (&argsbuf))
> + {
> + Xprintf_buffer_mark_failed (buf);
> + goto all_done;
> + }
> + args_value = argsbuf.data;
> + /* Set up the remaining two arrays to each point past the end of
> + the prior array, since space for all three has been allocated
> + now. */
> + args_size = &args_value[nargs].pa_int;
> + args_type = &args_size[nargs];
> + args_pa_user = &args_type[nargs] + args_pa_user_offset;
> + }
> + args_value[cnt].pa_user = args_pa_user;
> + args_pa_user += args_size[cnt];
> (*__printf_va_arg_table[args_type[cnt] - PA_LAST])
> (args_value[cnt].pa_user, ap_savep);
> }
--
Cheers,
Carlos.
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