[PATCH RFC v2] mm: move security_mmap_file() back into do_mmap()
Shu Han
ebpqwerty472123 at gmail.com
Wed Sep 25 11:57:01 UTC 2024
This patch moves the security_mmap_file() back into do_mmap(), which
revert(It is conceptually a revert of the commit(revert the feature
change in the commit), but not in the git sense(revert lines))
the commit 8b3ec6814c83d76b85bd13badc48552836c24839
("take security_mmap_file() outside of ->mmap_sem"). Below is the reason.
Some logic may call do_mmap() without calling security_mmap_file(),
without being aware of the harm this poses to LSM.
For example, CVE-2016-10044[1] was reported many years ago, but the
remap_file_pages() can still bypass the W^X policy enforced by SELinux[2]
for a long time.
Adding checks is easy(and has been done in all required call sites for
the current version), but there may have more calls to do_mmap() in the
future. Moving security_mmap_file() back into do_mmap() can avoid
forgetting, and avoid repeated logic for whether READ_IMPLIES_EXEC should
add PROT_EXEC for the mapping or not(In current, the !MMU case won't
imply exec if the file's mmap_capabilities is not exist, but the
security check logic is different).
It is noteworthy that moving the security check in do_mmap() will let it
in the mmap_write_lock, which slows down the performance and even have
deadlocks if someone depends on it(Since security_file_mprotect() is
already in the lock, this possibility is tiny), which requires LSM modules
to check.
Link: https://project-zero.issues.chromium.org/issues/42452389 [1]
Link: https://lore.kernel.org/all/20240919080905.4506-2-paul@paul-moore.com/ [2]
Signed-off-by: Shu Han <ebpqwerty472123 at gmail.com>
---
V2: Add RFC tag as lorenzo.stoakes at oracle.com suggested, and refine the
comment in patch.
V1: https://lore.kernel.org/all/20240925081628.408-1-ebpqwerty472123@gmail.com/
Alternatives:
1. mm: move the check of READ_IMPLIES_EXEC out of do_mmap()
2. Add sufficient comments for do_mmap()
---
include/linux/security.h | 8 ++++----
ipc/shm.c | 4 ----
mm/mmap.c | 9 +++++----
mm/nommu.c | 5 ++++-
mm/util.c | 19 ++++++++-----------
security/security.c | 41 ++++------------------------------------
6 files changed, 25 insertions(+), 61 deletions(-)
diff --git a/include/linux/security.h b/include/linux/security.h
index c37c32ebbdcd..e061bc9a0331 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -423,8 +423,8 @@ void security_file_free(struct file *file);
int security_file_ioctl(struct file *file, unsigned int cmd, unsigned long arg);
int security_file_ioctl_compat(struct file *file, unsigned int cmd,
unsigned long arg);
-int security_mmap_file(struct file *file, unsigned long prot,
- unsigned long flags);
+int security_mmap_file(struct file *file, unsigned long reqprot,
+ unsigned long prot, unsigned long flags);
int security_mmap_addr(unsigned long addr);
int security_file_mprotect(struct vm_area_struct *vma, unsigned long reqprot,
unsigned long prot);
@@ -1077,8 +1077,8 @@ static inline int security_file_ioctl_compat(struct file *file,
return 0;
}
-static inline int security_mmap_file(struct file *file, unsigned long prot,
- unsigned long flags)
+static inline int security_mmap_file(struct file *file, unsigned long reqprot,
+ unsigned long prot, unsigned long flags)
{
return 0;
}
diff --git a/ipc/shm.c b/ipc/shm.c
index 3e3071252dac..ce02560b856f 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -1636,10 +1636,6 @@ long do_shmat(int shmid, char __user *shmaddr, int shmflg,
sfd->vm_ops = NULL;
file->private_data = sfd;
- err = security_mmap_file(file, prot, flags);
- if (err)
- goto out_fput;
-
if (mmap_write_lock_killable(current->mm)) {
err = -EINTR;
goto out_fput;
diff --git a/mm/mmap.c b/mm/mmap.c
index 18fddcce03b8..56f9520f85ab 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1260,6 +1260,7 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
{
struct mm_struct *mm = current->mm;
int pkey = 0;
+ unsigned long reqprot = prot, err;
*populate = 0;
@@ -1276,6 +1277,10 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
if (!(file && path_noexec(&file->f_path)))
prot |= PROT_EXEC;
+ err = security_mmap_file(file, reqprot, prot, flags);
+ if (err)
+ return err;
+
/* force arch specific MAP_FIXED handling in get_unmapped_area */
if (flags & MAP_FIXED_NOREPLACE)
flags |= MAP_FIXED;
@@ -3198,12 +3203,8 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
flags |= MAP_LOCKED;
file = get_file(vma->vm_file);
- ret = security_mmap_file(vma->vm_file, prot, flags);
- if (ret)
- goto out_fput;
ret = do_mmap(vma->vm_file, start, size,
prot, flags, 0, pgoff, &populate, NULL);
-out_fput:
fput(file);
out:
mmap_write_unlock(mm);
diff --git a/mm/nommu.c b/mm/nommu.c
index 7296e775e04e..e632f3105a5a 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -681,7 +681,7 @@ static int validate_mmap_request(struct file *file,
unsigned long pgoff,
unsigned long *_capabilities)
{
- unsigned long capabilities, rlen;
+ unsigned long capabilities, rlen, reqprot = prot;
int ret;
/* do the simple checks first */
@@ -818,6 +818,9 @@ static int validate_mmap_request(struct file *file,
}
/* allow the security API to have its say */
+ ret = security_mmap_file(file, reqprot, prot, flags);
+ if (ret < 0)
+ return ret;
ret = security_mmap_addr(addr);
if (ret < 0)
return ret;
diff --git a/mm/util.c b/mm/util.c
index bd283e2132e0..47345e927a8f 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -581,17 +581,14 @@ unsigned long vm_mmap_pgoff(struct file *file, unsigned long addr,
unsigned long populate;
LIST_HEAD(uf);
- ret = security_mmap_file(file, prot, flag);
- if (!ret) {
- if (mmap_write_lock_killable(mm))
- return -EINTR;
- ret = do_mmap(file, addr, len, prot, flag, 0, pgoff, &populate,
- &uf);
- mmap_write_unlock(mm);
- userfaultfd_unmap_complete(mm, &uf);
- if (populate)
- mm_populate(ret, populate);
- }
+ if (mmap_write_lock_killable(mm))
+ return -EINTR;
+ ret = do_mmap(file, addr, len, prot, flag, 0, pgoff, &populate,
+ &uf);
+ mmap_write_unlock(mm);
+ userfaultfd_unmap_complete(mm, &uf);
+ if (populate)
+ mm_populate(ret, populate);
return ret;
}
diff --git a/security/security.c b/security/security.c
index 4564a0a1e4ef..25556629f588 100644
--- a/security/security.c
+++ b/security/security.c
@@ -2927,42 +2927,10 @@ int security_file_ioctl_compat(struct file *file, unsigned int cmd,
}
EXPORT_SYMBOL_GPL(security_file_ioctl_compat);
-static inline unsigned long mmap_prot(struct file *file, unsigned long prot)
-{
- /*
- * Does we have PROT_READ and does the application expect
- * it to imply PROT_EXEC? If not, nothing to talk about...
- */
- if ((prot & (PROT_READ | PROT_EXEC)) != PROT_READ)
- return prot;
- if (!(current->personality & READ_IMPLIES_EXEC))
- return prot;
- /*
- * if that's an anonymous mapping, let it.
- */
- if (!file)
- return prot | PROT_EXEC;
- /*
- * ditto if it's not on noexec mount, except that on !MMU we need
- * NOMMU_MAP_EXEC (== VM_MAYEXEC) in this case
- */
- if (!path_noexec(&file->f_path)) {
-#ifndef CONFIG_MMU
- if (file->f_op->mmap_capabilities) {
- unsigned caps = file->f_op->mmap_capabilities(file);
- if (!(caps & NOMMU_MAP_EXEC))
- return prot;
- }
-#endif
- return prot | PROT_EXEC;
- }
- /* anything on noexec mount won't get PROT_EXEC */
- return prot;
-}
-
/**
* security_mmap_file() - Check if mmap'ing a file is allowed
* @file: file
+ * @reqprot: protection requested by user
* @prot: protection applied by the kernel
* @flags: flags
*
@@ -2971,11 +2939,10 @@ static inline unsigned long mmap_prot(struct file *file, unsigned long prot)
*
* Return: Returns 0 if permission is granted.
*/
-int security_mmap_file(struct file *file, unsigned long prot,
- unsigned long flags)
+int security_mmap_file(struct file *file, unsigned long reqprot,
+ unsigned long prot, unsigned long flags)
{
- return call_int_hook(mmap_file, file, prot, mmap_prot(file, prot),
- flags);
+ return call_int_hook(mmap_file, file, reqprot, prot, flags);
}
/**
base-commit: f89722faa31466ff41aed21bdeb9cf34c2312858
--
2.34.1
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