diff options
| author | Jann Horn <jannh@google.com> | 2018-06-25 18:34:19 +0200 |
|---|---|---|
| committer | Eric W. Biederman <ebiederm@xmission.com> | 2018-08-11 02:05:53 -0500 |
| commit | 5820f140edef111a9ea2ef414ab2428b8cb805b1 (patch) | |
| tree | 3c8f89bbc5c3dcf1bdc0713dd1bcd1d9997c5da4 /kernel | |
| parent | 355139a8dba446cc11a424cddbf7afebc3041ba1 (diff) | |
userns: move user access out of the mutex
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@vger.kernel.org
Signed-off-by: Jann Horn <jannh@google.com>
Acked-by: Christian Brauner <christian@brauner.io>
Acked-by: Serge Hallyn <serge@hallyn.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/user_namespace.c | 24 |
1 files changed, 10 insertions, 14 deletions
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c index c3d7583fcd21..e5222b5fb4fe 100644 --- a/kernel/user_namespace.c +++ b/kernel/user_namespace.c @@ -859,7 +859,16 @@ static ssize_t map_write(struct file *file, const char __user *buf, unsigned idx; struct uid_gid_extent extent; 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. @@ -895,19 +904,6 @@ static ssize_t map_write(struct file *file, const char __user *buf, 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; |