Patch "io_uring/msg_ring: Fix NULL pointer dereference in io_msg_send_fd()" has been added to the 6.0-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    io_uring/msg_ring: Fix NULL pointer dereference in io_msg_send_fd()

to the 6.0-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     io_uring-msg_ring-fix-null-pointer-dereference-in-io.patch
and it can be found in the queue-6.0 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit ba0f0d84fe7b907900c88c664bce4e6c3542a52a
Author: Harshit Mogalapalli <harshit.m.mogalapalli@xxxxxxxxxx>
Date:   Wed Oct 19 10:12:18 2022 -0700

    io_uring/msg_ring: Fix NULL pointer dereference in io_msg_send_fd()
    
    [ Upstream commit 16bbdfe5fb0e78e0acb13e45fc127e9a296913f2 ]
    
    Syzkaller produced the below call trace:
    
     BUG: KASAN: null-ptr-deref in io_msg_ring+0x3cb/0x9f0
     Write of size 8 at addr 0000000000000070 by task repro/16399
    
     CPU: 0 PID: 16399 Comm: repro Not tainted 6.1.0-rc1 #28
     Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.11.0-2.el7
     Call Trace:
      <TASK>
      dump_stack_lvl+0xcd/0x134
      ? io_msg_ring+0x3cb/0x9f0
      kasan_report+0xbc/0xf0
      ? io_msg_ring+0x3cb/0x9f0
      kasan_check_range+0x140/0x190
      io_msg_ring+0x3cb/0x9f0
      ? io_msg_ring_prep+0x300/0x300
      io_issue_sqe+0x698/0xca0
      io_submit_sqes+0x92f/0x1c30
      __do_sys_io_uring_enter+0xae4/0x24b0
    ....
     RIP: 0033:0x7f2eaf8f8289
     RSP: 002b:00007fff40939718 EFLAGS: 00000246 ORIG_RAX: 00000000000001aa
     RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f2eaf8f8289
     RDX: 0000000000000000 RSI: 0000000000006f71 RDI: 0000000000000004
     RBP: 00007fff409397a0 R08: 0000000000000000 R09: 0000000000000039
     R10: 0000000000000000 R11: 0000000000000246 R12: 00000000004006d0
     R13: 00007fff40939880 R14: 0000000000000000 R15: 0000000000000000
      </TASK>
     Kernel panic - not syncing: panic_on_warn set ...
    
    We don't have a NULL check on file_ptr in io_msg_send_fd() function,
    so when file_ptr is NUL src_file is also NULL and get_file()
    dereferences a NULL pointer and leads to above crash.
    
    Add a NULL check to fix this issue.
    
    Fixes: e6130eba8a84 ("io_uring: add support for passing fixed file descriptors")
    Reported-by: syzkaller <syzkaller@xxxxxxxxxxxxxxxx>
    Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@xxxxxxxxxx>
    Link: https://lore.kernel.org/r/20221019171218.1337614-1-harshit.m.mogalapalli@xxxxxxxxxx
    Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/io_uring/msg_ring.c b/io_uring/msg_ring.c
index 4a7e5d030c78..90d2fc6fd80e 100644
--- a/io_uring/msg_ring.c
+++ b/io_uring/msg_ring.c
@@ -95,6 +95,9 @@ static int io_msg_send_fd(struct io_kiocb *req, unsigned int issue_flags)
 
 	msg->src_fd = array_index_nospec(msg->src_fd, ctx->nr_user_files);
 	file_ptr = io_fixed_file_slot(&ctx->file_table, msg->src_fd)->file_ptr;
+	if (!file_ptr)
+		goto out_unlock;
+
 	src_file = (struct file *) (file_ptr & FFS_MASK);
 	get_file(src_file);