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iomap: fix WARN_ON_ONCE() from unprivileged users

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It is trivial to trigger a WARN_ON_ONCE(1) in iomap_dio_actor() by
unprivileged users which would taint the kernel, or worse - panic if
panic_on_warn or panic_on_taint is set. Hence, just convert it to
pr_warn_ratelimited() to let users know their workloads are racing.
Thank Dave Chinner for the initial analysis of the racing reproducers.

Signed-off-by: Qian Cai <cai@lca.pw>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
This commit is contained in:
Qian Cai 2020-09-10 08:26:15 -07:00 committed by Darrick J. Wong
parent f4d51dffc6
commit a805c11165
1 changed files with 10 additions and 0 deletions
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10
fs/iomap/direct-io.c
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@ -388,6 +388,16 @@ iomap_dio_actor(struct inode *inode, loff_t pos, loff_t length,
return iomap_dio_bio_actor(inode, pos, length, dio, iomap);
case IOMAP_INLINE:
return iomap_dio_inline_actor(inode, pos, length, dio, iomap);
case IOMAP_DELALLOC:
/*
* DIO is not serialised against mmap() access at all, and so
* if the page_mkwrite occurs between the writeback and the
* iomap_apply() call in the DIO path, then it will see the
* DELALLOC block that the page-mkwrite allocated.
*/
pr_warn_ratelimited("Direct I/O collision with buffered writes! File: %pD4 Comm: %.20s\n",
dio->iocb->ki_filp, current->comm);
return -EIO;
default:
WARN_ON_ONCE(1);
return -EIO;