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authorJann Horn <jannh@google.com>2018-06-25 18:34:19 +0200
committerEric W. Biederman <ebiederm@xmission.com>2018-08-11 02:05:53 -0500
commit5820f140edef111a9ea2ef414ab2428b8cb805b1 (patch)
tree3c8f89bbc5c3dcf1bdc0713dd1bcd1d9997c5da4
parent355139a8dba446cc11a424cddbf7afebc3041ba1 (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>
-rw-r--r--kernel/user_namespace.c24
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;