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prctl: fix PR_SET_MM_AUXV kernel stack leak 

Doing a

	prctl(PR_SET_MM, PR_SET_MM_AUXV, addr, 1);

will copy 1 byte from userspace to (quite big) on-stack array
and then stash everything to mm->saved_auxv.
AT_NULL terminator will be inserted at the very end.

/proc/*/auxv handler will find that AT_NULL terminator
and copy original stack contents to userspace.

This devious scheme requires CAP_SYS_RESOURCE.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Alexey Dobriyan 2021-03-14 23:51:14 +03:00 committed by Linus Torvalds
parent 70404fe303
commit c995f12ad8
1 changed files with 1 additions and 1 deletions
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2
kernel/sys.c
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@ -2079,7 +2079,7 @@ static int prctl_set_auxv(struct mm_struct *mm, unsigned long addr,
* up to the caller to provide sane values here, otherwise userspace
* tools which use this vector might be unhappy.
*/
unsigned long user_auxv[AT_VECTOR_SIZE];
unsigned long user_auxv[AT_VECTOR_SIZE] = {};
if (len > sizeof(user_auxv))
return -EINVAL;