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authorLino Sanfilippo <LinoSanfilippo@gmx.de>2013-07-08 15:59:42 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2013-07-09 10:33:19 -0700
commit7b18527c4a95397b443c8c22f75634d5d11c9d47 (patch)
treea701ab062a6f00f8e5c11851ca482b687f65ef10 /fs/notify
parentde1e0c40aceb9d5bff09c3a3b97b2f1b178af53f (diff)
downloadlinux-linaro-stable-7b18527c4a95397b443c8c22f75634d5d11c9d47.tar.gz
fanotify: fix races when adding/removing marks
For both adding an event to an existing mark and destroying a mark we first have to find it via fsnotify_find_[inode|vfsmount]_mark(). But getting the mark and adding an event (or destroying it) is not done atomically. This opens a race where a thread is about to destroy a mark while another thread still finds the same mark and adds an event to its mask although it will be destroyed. Another race exists concerning the excess of a groups number of marks limit: When a mark is added the number of group marks is checked against the max number of marks per group and increased afterwards. Since check and increment is also not done atomically, this may result in 2 or more processes passing the check at the same time and increasing the number of group marks above the allowed limit. With this patch both races are avoided by doing the concerning operations with the groups mark mutex locked. Signed-off-by: Lino Sanfilippo <LinoSanfilippo@gmx.de> Cc: Eric Paris <eparis@redhat.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'fs/notify')
-rw-r--r--fs/notify/fanotify/fanotify_user.c49
1 files changed, 37 insertions, 12 deletions
diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
index e16076d386c4..4e1d8ec77b04 100644
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c
@@ -524,14 +524,18 @@ static int fanotify_remove_vfsmount_mark(struct fsnotify_group *group,
__u32 removed;
int destroy_mark;
+ mutex_lock(&group->mark_mutex);
fsn_mark = fsnotify_find_vfsmount_mark(group, mnt);
- if (!fsn_mark)
+ if (!fsn_mark) {
+ mutex_unlock(&group->mark_mutex);
return -ENOENT;
+ }
removed = fanotify_mark_remove_from_mask(fsn_mark, mask, flags,
&destroy_mark);
if (destroy_mark)
- fsnotify_destroy_mark(fsn_mark, group);
+ fsnotify_destroy_mark_locked(fsn_mark, group);
+ mutex_unlock(&group->mark_mutex);
fsnotify_put_mark(fsn_mark);
if (removed & real_mount(mnt)->mnt_fsnotify_mask)
@@ -548,14 +552,19 @@ static int fanotify_remove_inode_mark(struct fsnotify_group *group,
__u32 removed;
int destroy_mark;
+ mutex_lock(&group->mark_mutex);
fsn_mark = fsnotify_find_inode_mark(group, inode);
- if (!fsn_mark)
+ if (!fsn_mark) {
+ mutex_unlock(&group->mark_mutex);
return -ENOENT;
+ }
removed = fanotify_mark_remove_from_mask(fsn_mark, mask, flags,
&destroy_mark);
if (destroy_mark)
- fsnotify_destroy_mark(fsn_mark, group);
+ fsnotify_destroy_mark_locked(fsn_mark, group);
+ mutex_unlock(&group->mark_mutex);
+
/* matches the fsnotify_find_inode_mark() */
fsnotify_put_mark(fsn_mark);
if (removed & inode->i_fsnotify_mask)
@@ -599,21 +608,29 @@ static int fanotify_add_vfsmount_mark(struct fsnotify_group *group,
__u32 added;
int ret = 0;
+ mutex_lock(&group->mark_mutex);
fsn_mark = fsnotify_find_vfsmount_mark(group, mnt);
if (!fsn_mark) {
- if (atomic_read(&group->num_marks) > group->fanotify_data.max_marks)
+ if (atomic_read(&group->num_marks) > group->fanotify_data.max_marks) {
+ mutex_unlock(&group->mark_mutex);
return -ENOSPC;
+ }
fsn_mark = kmem_cache_alloc(fanotify_mark_cache, GFP_KERNEL);
- if (!fsn_mark)
+ if (!fsn_mark) {
+ mutex_unlock(&group->mark_mutex);
return -ENOMEM;
+ }
fsnotify_init_mark(fsn_mark, fanotify_free_mark);
- ret = fsnotify_add_mark(fsn_mark, group, NULL, mnt, 0);
- if (ret)
+ ret = fsnotify_add_mark_locked(fsn_mark, group, NULL, mnt, 0);
+ if (ret) {
+ mutex_unlock(&group->mark_mutex);
goto err;
+ }
}
added = fanotify_mark_add_to_mask(fsn_mark, mask, flags);
+ mutex_unlock(&group->mark_mutex);
if (added & ~real_mount(mnt)->mnt_fsnotify_mask)
fsnotify_recalc_vfsmount_mask(mnt);
@@ -642,21 +659,29 @@ static int fanotify_add_inode_mark(struct fsnotify_group *group,
(atomic_read(&inode->i_writecount) > 0))
return 0;
+ mutex_lock(&group->mark_mutex);
fsn_mark = fsnotify_find_inode_mark(group, inode);
if (!fsn_mark) {
- if (atomic_read(&group->num_marks) > group->fanotify_data.max_marks)
+ if (atomic_read(&group->num_marks) > group->fanotify_data.max_marks) {
+ mutex_unlock(&group->mark_mutex);
return -ENOSPC;
+ }
fsn_mark = kmem_cache_alloc(fanotify_mark_cache, GFP_KERNEL);
- if (!fsn_mark)
+ if (!fsn_mark) {
+ mutex_unlock(&group->mark_mutex);
return -ENOMEM;
+ }
fsnotify_init_mark(fsn_mark, fanotify_free_mark);
- ret = fsnotify_add_mark(fsn_mark, group, inode, NULL, 0);
- if (ret)
+ ret = fsnotify_add_mark_locked(fsn_mark, group, inode, NULL, 0);
+ if (ret) {
+ mutex_unlock(&group->mark_mutex);
goto err;
+ }
}
added = fanotify_mark_add_to_mask(fsn_mark, mask, flags);
+ mutex_unlock(&group->mark_mutex);
if (added & ~inode->i_fsnotify_mask)
fsnotify_recalc_inode_mask(inode);