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userns: move user access out of the mutex 

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: 22d917d80e ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Jann Horn 2018-06-25 18:34:19 +02:00 committed by syphyr
parent c019ab8a11
commit f404acaf7f
1 changed files with 19 additions and 20 deletions
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39
kernel/user_namespace.c
View File

@ -595,9 +595,26 @@ static ssize_t map_write(struct file *file, const char __user *buf,
struct uid_gid_map new_map;
unsigned idx;
struct uid_gid_extent *extent = NULL;
unsigned long page = 0;
unsigned long page;
char *kbuf, *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;
/* Get a buffer */
page = __get_free_page(GFP_TEMPORARY);
kbuf = (char *) page;
if (!page)
return -ENOMEM;
/* Slurp in the user data */
if (copy_from_user(kbuf, buf, count)) {
free_page(page);
return -EFAULT;
}
kbuf[count] = '\0';
/*
* The userns_state_mutex serializes all writes to any given map.
@ -631,24 +648,6 @@ 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;
/* Get a buffer */
ret = -ENOMEM;
page = __get_free_page(GFP_TEMPORARY);
kbuf = (char *) page;
if (!page)
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 */
ret = -EFAULT;
if (copy_from_user(kbuf, buf, count))
goto out;
kbuf[count] = '\0';
/* Parse the user data */
ret = -EINVAL;
pos = kbuf;