When argmin was added in commit 655c16a8ce9c ("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@xxxxxxxxxx [1]
Link: https://lore.kernel.org/all/202406211253.7037F69@keescook/ [2]
Signed-off-by: Kees Cook <kees@xxxxxxxxxx>
---
Cc: Guenter Roeck <linux@xxxxxxxxxxxx>
Cc: Eric Biederman <ebiederm@xxxxxxxxxxxx>
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Christian Brauner <brauner@xxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Alexey Dobriyan <adobriyan@xxxxxxxxx>
Cc: Laurent Vivier <laurent@xxxxxxxxx>
Cc: Lukas Bulwahn <lukas.bulwahn@xxxxxxxxx>
Cc: linux-fsdevel@xxxxxxxxxxxxxxx
Cc: linux-mm@xxxxxxxxx
---
fs/exec.c | 26 ++++++++++++++++++++------
fs/exec_test.c | 2 ++
include/linux/binfmts.h | 2 +-
3 files changed, 23 insertions(+), 7 deletions(-)
diff --git a/fs/exec.c b/fs/exec.c
index c3bec126505b..b7bc63bfb907 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -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) {
diff --git a/fs/exec_test.c b/fs/exec_test.c
index 32a90c6f47e7..8fea0bf0b7f5 100644
--- a/fs/exec_test.c
+++ b/fs/exec_test.c
@@ -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
}
}
diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h
index 70f97f685bff..e6c00e860951 100644
--- a/include/linux/binfmts.h
+++ b/include/linux/binfmts.h
@@ -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,
--
2.34.1
