4.9-stable review patch. If anyone has any objections, please let me know.
------------------
From: Jann Horn <jannh@xxxxxxxxxx>
commit 5820f140edef111a9ea2ef414ab2428b8cb805b1 upstream.
The old code would hold the userns_state_mutex indefinitely if
memdup_user_nul stalled due to e.g. a userfault region. Prevent that by
moving the memdup_user_nul in front of the mutex_lock().
Note: This changes the error precedence of invalid buf/count/*ppos vs
map already written / capabilities missing.
Fixes: 22d917d80e84 ("userns: Rework the user_namespace adding uid/gid...")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Jann Horn <jannh@xxxxxxxxxx>
Acked-by: Christian Brauner <christian@xxxxxxxxxx>
Acked-by: Serge Hallyn <serge@xxxxxxxxxx>
Signed-off-by: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/user_namespace.c | 24 ++++++++++--------------
1 file changed, 10 insertions(+), 14 deletions(-)
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -649,7 +649,16 @@ static ssize_t map_write(struct file *fi
unsigned idx;
struct uid_gid_extent *extent = NULL;
char *kbuf = NULL, *pos, *next_line;
- ssize_t ret = -EINVAL;
+ ssize_t ret;
+
+ /* Only allow < page size writes at the beginning of the file */
+ if ((*ppos != 0) || (count >= PAGE_SIZE))
+ return -EINVAL;
+
+ /* Slurp in the user data */
+ kbuf = memdup_user_nul(buf, count);
+ if (IS_ERR(kbuf))
+ return PTR_ERR(kbuf);
/*
* The userns_state_mutex serializes all writes to any given map.
@@ -683,19 +692,6 @@ static ssize_t map_write(struct file *fi
if (cap_valid(cap_setid) && !file_ns_capable(file, ns, CAP_SYS_ADMIN))
goto out;
- /* Only allow < page size writes at the beginning of the file */
- ret = -EINVAL;
- if ((*ppos != 0) || (count >= PAGE_SIZE))
- goto out;
-
- /* Slurp in the user data */
- kbuf = memdup_user_nul(buf, count);
- if (IS_ERR(kbuf)) {
- ret = PTR_ERR(kbuf);
- kbuf = NULL;
- goto out;
- }
-
/* Parse the user data */
ret = -EINVAL;
pos = kbuf;
