Commit 656d6e6f authored by Jann Horn's avatar Jann Horn Committed by Greg Kroah-Hartman

userns: move user access out of the mutex

commit 5820f140 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: 22d917d8 ("userns: Rework the user_namespace adding uid/gid...")
Cc: stable@vger.kernel.org
Signed-off-by: default avatarJann Horn <jannh@google.com>
Acked-by: default avatarChristian Brauner <christian@brauner.io>
Acked-by: default avatarSerge Hallyn <serge@hallyn.com>
Signed-off-by: default avatarEric W. Biederman <ebiederm@xmission.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent b692c405
......@@ -650,7 +650,16 @@ static ssize_t map_write(struct file *file, const char __user *buf,
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.
......@@ -684,19 +693,6 @@ 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;
......
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