Patch "io_uring/rsrc: fix null-ptr-deref in io_file_bitmap_get()" has been added to the 6.2-stable tree

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

    io_uring/rsrc: fix null-ptr-deref in io_file_bitmap_get()

to the 6.2-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-rsrc-fix-null-ptr-deref-in-io_file_bitmap_get.patch
and it can be found in the queue-6.2 subdirectory.

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


>From 02a4d923e4400a36d340ea12d8058f69ebf3a383 Mon Sep 17 00:00:00 2001
From: Savino Dicanosa <sd7.dev@xxxxx>
Date: Tue, 21 Mar 2023 19:44:02 +0000
Subject: io_uring/rsrc: fix null-ptr-deref in io_file_bitmap_get()

From: Savino Dicanosa <sd7.dev@xxxxx>

commit 02a4d923e4400a36d340ea12d8058f69ebf3a383 upstream.

When fixed files are unregistered, file_alloc_end and alloc_hint
are not cleared. This can later cause a NULL pointer dereference in
io_file_bitmap_get() if auto index selection is enabled via
IORING_FILE_INDEX_ALLOC:

[    6.519129] BUG: kernel NULL pointer dereference, address: 0000000000000000
[...]
[    6.541468] RIP: 0010:_find_next_zero_bit+0x1a/0x70
[...]
[    6.560906] Call Trace:
[    6.561322]  <TASK>
[    6.561672]  io_file_bitmap_get+0x38/0x60
[    6.562281]  io_fixed_fd_install+0x63/0xb0
[    6.562851]  ? __pfx_io_socket+0x10/0x10
[    6.563396]  io_socket+0x93/0xf0
[    6.563855]  ? __pfx_io_socket+0x10/0x10
[    6.564411]  io_issue_sqe+0x5b/0x3d0
[    6.564914]  io_submit_sqes+0x1de/0x650
[    6.565452]  __do_sys_io_uring_enter+0x4fc/0xb20
[    6.566083]  ? __do_sys_io_uring_register+0x11e/0xd80
[    6.566779]  do_syscall_64+0x3c/0x90
[    6.567247]  entry_SYSCALL_64_after_hwframe+0x72/0xdc
[...]

To fix the issue, set file alloc range and alloc_hint to zero after
file tables are freed.

Cc: stable@xxxxxxxxxxxxxxx
Fixes: 4278a0deb1f6 ("io_uring: defer alloc_hint update to io_file_bitmap_set()")
Signed-off-by: Savino Dicanosa <sd7.dev@xxxxx>
[axboe: add explicit bitmap == NULL check as well]
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 io_uring/filetable.c |    3 +++
 io_uring/rsrc.c      |    1 +
 2 files changed, 4 insertions(+)

--- a/io_uring/filetable.c
+++ b/io_uring/filetable.c
@@ -19,6 +19,9 @@ static int io_file_bitmap_get(struct io_
 	unsigned long nr = ctx->file_alloc_end;
 	int ret;
 
+	if (!table->bitmap)
+		return -ENFILE;
+
 	do {
 		ret = find_next_zero_bit(table->bitmap, nr, table->alloc_hint);
 		if (ret != nr)
--- a/io_uring/rsrc.c
+++ b/io_uring/rsrc.c
@@ -794,6 +794,7 @@ void __io_sqe_files_unregister(struct io
 	}
 #endif
 	io_free_file_tables(&ctx->file_table);
+	io_file_table_set_alloc_range(ctx, 0, 0);
 	io_rsrc_data_free(ctx->file_data);
 	ctx->file_data = NULL;
 	ctx->nr_user_files = 0;


Patches currently in stable-queue which might be from sd7.dev@xxxxx are

queue-6.2/io_uring-rsrc-fix-null-ptr-deref-in-io_file_bitmap_get.patch



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