diff options
| author | NeilBrown | 2017-04-03 11:30:34 +1000 |
|---|---|---|
| committer | Greg Kroah-Hartman | 2017-04-08 17:33:32 +0200 |
| commit | c8a139d001a1aab1ea8734db14b22dac9dd143b6 (patch) | |
| tree | c036998a6ca7946d3bac2485838245edac07ee8d /fs | |
| parent | cf903e9d3a97f89b224d2d07be37c0f160db8192 (diff) | |
sysfs: be careful of error returns from ops->show()
ops->show() can return a negative error code.
Commit 65da3484d9be ("sysfs: correctly handle short reads on PREALLOC attrs.")
(in v4.4) caused this to be stored in an unsigned 'size_t' variable, so errors
would look like large numbers.
As a result, if an error is returned, sysfs_kf_read() will return the
value of 'count', typically 4096.
Commit 17d0774f8068 ("sysfs: correctly handle read offset on PREALLOC attrs")
(in v4.8) extended this error to use the unsigned large 'len' as a size for
memmove().
Consequently, if ->show returns an error, then the first read() on the
sysfs file will return 4096 and could return uninitialized memory to
user-space.
If the application performs a subsequent read, this will trigger a memmove()
with extremely large count, and is likely to crash the machine is bizarre ways.
This bug can currently only be triggered by reading from an md
sysfs attribute declared with __ATTR_PREALLOC() during the
brief period between when mddev_put() deletes an mddev from
the ->all_mddevs list, and when mddev_delayed_delete() - which is
scheduled on a workqueue - completes.
Before this, an error won't be returned by the ->show()
After this, the ->show() won't be called.
I can reproduce it reliably only by putting delay like
usleep_range(500000,700000);
early in mddev_delayed_delete(). Then after creating an
md device md0 run
echo clear > /sys/block/md0/md/array_state; cat /sys/block/md0/md/array_state
The bug can be triggered without the usleep.
Fixes: 65da3484d9be ("sysfs: correctly handle short reads on PREALLOC attrs.")
Fixes: 17d0774f8068 ("sysfs: correctly handle read offset on PREALLOC attrs")
Cc: stable@vger.kernel.org
Signed-off-by: NeilBrown <neilb@suse.com>
Acked-by: Tejun Heo <tj@kernel.org>
Reported-and-tested-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'fs')
| -rw-r--r-- | fs/sysfs/file.c | 6 |
1 files changed, 4 insertions, 2 deletions
diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c index b803213d1307..39c75a86c67f 100644 --- a/fs/sysfs/file.c +++ b/fs/sysfs/file.c @@ -108,7 +108,7 @@ static ssize_t sysfs_kf_read(struct kernfs_open_file *of, char *buf, { const struct sysfs_ops *ops = sysfs_file_ops(of->kn); struct kobject *kobj = of->kn->parent->priv; - size_t len; + ssize_t len; /* * If buf != of->prealloc_buf, we don't know how @@ -117,13 +117,15 @@ static ssize_t sysfs_kf_read(struct kernfs_open_file *of, char *buf, if (WARN_ON_ONCE(buf != of->prealloc_buf)) return 0; len = ops->show(kobj, of->kn->priv, buf); + if (len < 0) + return len; if (pos) { if (len <= pos) return 0; len -= pos; memmove(buf, buf + pos, len); } - return min(count, len); + return min_t(ssize_t, count, len); } /* kernfs write callback for regular sysfs files */ |