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execve: Keep bprm->argmin behind CONFIG_MMU

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When argmin was added in commit 655c16a8ce ("exec: separate
MM_ANONPAGES and RLIMIT_STACK accounting"), it was intended only for
validating stack limits on CONFIG_MMU[1]. All checking for reaching the
limit (argmin) is wrapped in CONFIG_MMU ifdef checks, though setting
argmin was not. That argmin is only supposed to be used under CONFIG_MMU
was rediscovered recently[2], and I don't want to trip over this again.

Move argmin's declaration into the existing CONFIG_MMU area, and add
helpers functions so the MMU tests can be consolidated.

Link: https://lore.kernel.org/all/20181126122307.GA1660@redhat.com [1]
Link: https://lore.kernel.org/all/202406211253.7037F69@keescook/ [2]
Link: https://lore.kernel.org/r/20240621205046.4001362-1-kees@kernel.org
Signed-off-by: Kees Cook <kees@kernel.org>
This commit is contained in:
Kees Cook 2024-06-21 13:50:43 -07:00
parent 2a97388a80
commit 084ebf7ca8
3 changed files with 23 additions and 7 deletions
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26
fs/exec.c
View File

@ -486,6 +486,23 @@ static int count_strings_kernel(const char *const *argv)
return i;
}
static inline int bprm_set_stack_limit(struct linux_binprm *bprm,
unsigned long limit)
{
#ifdef CONFIG_MMU
bprm->argmin = bprm->p - limit;
#endif
return 0;
}
static inline bool bprm_hit_stack_limit(struct linux_binprm *bprm)
{
#ifdef CONFIG_MMU
return bprm->p < bprm->argmin;
#else
return false;
#endif
}
/*
* Calculate bprm->argmin from:
* - _STK_LIM
@ -532,8 +549,7 @@ static int bprm_stack_limits(struct linux_binprm *bprm)
return -E2BIG;
limit -= ptr_size;
bprm->argmin = bprm->p - limit;
return 0;
return bprm_set_stack_limit(bprm, limit);
}
/*
@ -571,10 +587,8 @@ static int copy_strings(int argc, struct user_arg_ptr argv,
pos = bprm->p;
str += len;
bprm->p -= len;
#ifdef CONFIG_MMU
if (bprm->p < bprm->argmin)
if (bprm_hit_stack_limit(bprm))
goto out;
#endif
while (len > 0) {
int offset, bytes_to_copy;
@ -649,7 +663,7 @@ int copy_string_kernel(const char *arg, struct linux_binprm *bprm)
/* We're going to work our way backwards. */
arg += len;
bprm->p -= len;
if (IS_ENABLED(CONFIG_MMU) && bprm->p < bprm->argmin)
if (bprm_hit_stack_limit(bprm))
return -E2BIG;
while (len > 0) {

2
fs/exec_test.c
View File

@ -96,7 +96,9 @@ static void exec_test_bprm_stack_limits(struct kunit *test)
rc = bprm_stack_limits(&bprm);
KUNIT_EXPECT_EQ_MSG(test, rc, result->expected_rc, "on loop %d", i);
#ifdef CONFIG_MMU
KUNIT_EXPECT_EQ_MSG(test, bprm.argmin, result->expected_argmin, "on loop %d", i);
#endif
}
}

2
include/linux/binfmts.h
View File

@ -19,13 +19,13 @@ struct linux_binprm {
#ifdef CONFIG_MMU
struct vm_area_struct *vma;
unsigned long vma_pages;
unsigned long argmin; /* rlimit marker for copy_strings() */
#else
# define MAX_ARG_PAGES 32
struct page *page[MAX_ARG_PAGES];
#endif
struct mm_struct *mm;
unsigned long p; /* current top of mem */
unsigned long argmin; /* rlimit marker for copy_strings() */
unsigned int
/* Should an execfd be passed to userspace? */
have_execfd:1,