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authorArtem Bityutskiy <artem.bityutskiy@linux.intel.com>2013-06-28 14:15:15 +0300
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2013-07-03 10:59:05 -0700
commit4e3010bf3aab410b6a983fcd05fe65e671648f55 (patch)
tree3735783d6c4449ac29833f0ff9ef8731d45160de /fs
parenteafde0bc4fbb118408050b7f32dde3575930ef16 (diff)
UBIFS: fix a horrid bug
commit 605c912bb843c024b1ed173dc427cd5c08e5d54d upstream. Al Viro pointed me to the fact that '->readdir()' and '->llseek()' have no mutual exclusion, which means the 'ubifs_dir_llseek()' can be run while we are in the middle of 'ubifs_readdir()'. This means that 'file->private_data' can be freed while 'ubifs_readdir()' uses it, and this is a very bad bug: not only 'ubifs_readdir()' can return garbage, but this may corrupt memory and lead to all kinds of problems like crashes an security holes. This patch fixes the problem by using the 'file->f_version' field, which '->llseek()' always unconditionally sets to zero. We set it to 1 in 'ubifs_readdir()' and whenever we detect that it became 0, we know there was a seek and it is time to clear the state saved in 'file->private_data'. I tested this patch by writing a user-space program which runds readdir and seek in parallell. I could easily crash the kernel without these patches, but could not crash it with these patches. Reported-by: Al Viro <viro@zeniv.linux.org.uk> Tested-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com> Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'fs')
-rw-r--r--fs/ubifs/dir.c30
1 files changed, 27 insertions, 3 deletions
diff --git a/fs/ubifs/dir.c b/fs/ubifs/dir.c
index 83a7c00f565b..25c472bb8ab5 100644
--- a/fs/ubifs/dir.c
+++ b/fs/ubifs/dir.c
@@ -373,6 +373,24 @@ static int ubifs_readdir(struct file *file, void *dirent, filldir_t filldir)
*/
return 0;
+ if (file->f_version == 0) {
+ /*
+ * The file was seek'ed, which means that @file->private_data
+ * is now invalid. This may also be just the first
+ * 'ubifs_readdir()' invocation, in which case
+ * @file->private_data is NULL, and the below code is
+ * basically a no-op.
+ */
+ kfree(file->private_data);
+ file->private_data = NULL;
+ }
+
+ /*
+ * 'generic_file_llseek()' unconditionally sets @file->f_version to
+ * zero, and we use this for detecting whether the file was seek'ed.
+ */
+ file->f_version = 1;
+
/* File positions 0 and 1 correspond to "." and ".." */
if (pos == 0) {
ubifs_assert(!file->private_data);
@@ -446,6 +464,14 @@ static int ubifs_readdir(struct file *file, void *dirent, filldir_t filldir)
file->f_pos = pos = key_hash_flash(c, &dent->key);
file->private_data = dent;
cond_resched();
+
+ if (file->f_version == 0)
+ /*
+ * The file was seek'ed meanwhile, lets return and start
+ * reading direntries from the new position on the next
+ * invocation.
+ */
+ return 0;
}
out:
@@ -456,15 +482,13 @@ out:
kfree(file->private_data);
file->private_data = NULL;
+ /* 2 is a special value indicating that there are no more direntries */
file->f_pos = 2;
return 0;
}
-/* If a directory is seeked, we have to free saved readdir() state */
static loff_t ubifs_dir_llseek(struct file *file, loff_t offset, int origin)
{
- kfree(file->private_data);
- file->private_data = NULL;
return generic_file_llseek(file, offset, origin);
}