summaryrefslogtreecommitdiffstats
path: root/include
diff options
context:
space:
mode:
authorLinus Torvalds <torvalds@linux-foundation.org>2019-03-03 14:23:33 -0800
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2019-05-02 09:58:58 +0200
commitd6b2615f7d31d8e58b685d42dbafcc7dc1204bbd (patch)
treed27851ddb50806ef72a24e0b9b3fe7ae6c1a98fc /include
parent2afa01cd9186974051b38b7d1f31bb2407e41e3a (diff)
downloadlinux-stable-d6b2615f7d31d8e58b685d42dbafcc7dc1204bbd.tar.gz
linux-stable-d6b2615f7d31d8e58b685d42dbafcc7dc1204bbd.tar.bz2
linux-stable-d6b2615f7d31d8e58b685d42dbafcc7dc1204bbd.zip
aio: simplify - and fix - fget/fput for io_submit()
commit 84c4e1f89fefe70554da0ab33be72c9be7994379 upstream. Al Viro root-caused a race where the IOCB_CMD_POLL handling of fget/fput() could cause us to access the file pointer after it had already been freed: "In more details - normally IOCB_CMD_POLL handling looks so: 1) io_submit(2) allocates aio_kiocb instance and passes it to aio_poll() 2) aio_poll() resolves the descriptor to struct file by req->file = fget(iocb->aio_fildes) 3) aio_poll() sets ->woken to false and raises ->ki_refcnt of that aio_kiocb to 2 (bumps by 1, that is). 4) aio_poll() calls vfs_poll(). After sanity checks (basically, "poll_wait() had been called and only once") it locks the queue. That's what the extra reference to iocb had been for - we know we can safely access it. 5) With queue locked, we check if ->woken has already been set to true (by aio_poll_wake()) and, if it had been, we unlock the queue, drop a reference to aio_kiocb and bugger off - at that point it's a responsibility to aio_poll_wake() and the stuff called/scheduled by it. That code will drop the reference to file in req->file, along with the other reference to our aio_kiocb. 6) otherwise, we see whether we need to wait. If we do, we unlock the queue, drop one reference to aio_kiocb and go away - eventual wakeup (or cancel) will deal with the reference to file and with the other reference to aio_kiocb 7) otherwise we remove ourselves from waitqueue (still under the queue lock), so that wakeup won't get us. No async activity will be happening, so we can safely drop req->file and iocb ourselves. If wakeup happens while we are in vfs_poll(), we are fine - aio_kiocb won't get freed under us, so we can do all the checks and locking safely. And we don't touch ->file if we detect that case. However, vfs_poll() most certainly *does* touch the file it had been given. So wakeup coming while we are still in ->poll() might end up doing fput() on that file. That case is not too rare, and usually we are saved by the still present reference from descriptor table - that fput() is not the final one. But if another thread closes that descriptor right after our fget() and wakeup does happen before ->poll() returns, we are in trouble - final fput() done while we are in the middle of a method: Al also wrote a patch to take an extra reference to the file descriptor to fix this, but I instead suggested we just streamline the whole file pointer handling by submit_io() so that the generic aio submission code simply keeps the file pointer around until the aio has completed. Fixes: bfe4037e722e ("aio: implement IOCB_CMD_POLL") Acked-by: Al Viro <viro@zeniv.linux.org.uk> Reported-by: syzbot+503d4cc169fcec1cb18c@syzkaller.appspotmail.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Cc: Guenter Roeck <linux@roeck-us.net> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'include')
-rw-r--r--include/linux/fs.h8
1 files changed, 7 insertions, 1 deletions
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 7b6084854bfe..111c94c4baa1 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -304,13 +304,19 @@ enum rw_hint {
struct kiocb {
struct file *ki_filp;
+
+ /* The 'ki_filp' pointer is shared in a union for aio */
+ randomized_struct_fields_start
+
loff_t ki_pos;
void (*ki_complete)(struct kiocb *iocb, long ret, long ret2);
void *private;
int ki_flags;
u16 ki_hint;
u16 ki_ioprio; /* See linux/ioprio.h */
-} __randomize_layout;
+
+ randomized_struct_fields_end
+};
static inline bool is_sync_kiocb(struct kiocb *kiocb)
{