6.15-stable review patch. If anyone has any objections, please let me know.
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From: Nitesh Shetty nj.shetty@samsung.com
[ Upstream commit 334d7c4fb60cf21e0abac134d92fe49e9b04377e ]
If iov_offset is non-zero, then we need to consider iov_offset in length calculation, otherwise we might pass smaller IOs such as 512 bytes, in below scenario [1].
This issue is reproducible using lib-uring test/fixed-seg.c application with fixed buffer on a 512 LBA formatted device.
[1]
At present we pass the alignment check, for 512 LBA formatted devices, len_mask = 511 when IO is smaller, i->count = 512 has an offset, i->io_offset = 3584 with bvec values, bvec->bv_offset = 256, bvec->bv_len = 3840. In short, the first 256 bytes are in the current page, next 256 bytes are in the another page. Ideally we expect to fail the IO.
I can think of 2 userspace scenarios where we experience this.
a: From userspace, we observe a different behaviour when device LBA size is 512 vs 4096 bytes. For 4096 LBA formatted device, I see the same liburing test [2] failing, whereas 512 the test passes without this. This is reproducible everytime.
[2] https://github.com/axboe/liburing/
b: Although I was not able to reproduce the below condition, but I suspect below case should be possible from user space for devices with 512 LBA formatted device. Lets say from userspace while allocating a virtually single chunk of memory, if we get 2 physical chunk of memory, and IO happens to be at the boundary of first physical chunk with length crossing first chunk, then we allow IOs to proceed and hence we might map wrong physical address length and proceed with IO rather than failing.
: --- a/test/fixed-seg.c : +++ b/test/fixed-seg.c : @@ -64,7 +64,7 @@ static int test(struct io_uring *ring, int fd, int : vec_off) : return T_EXIT_FAIL; : } : : - ret = read_it(ring, fd, 4096, vec_off); : + ret = read_it(ring, fd, 4096, 7*512 + 256); : if (ret) { : fprintf(stderr, "4096 0 failed\n"); : return T_EXIT_FAIL;
Effectively this is a write crossing the page boundary.
Link: https://lkml.kernel.org/r/20250428095849.11709-1-nj.shetty@samsung.com Fixes: 2263639f96f2 ("iov_iter: streamline iovec/bvec alignment iteration") Reviewed-by: Jens Axboe axboe@kernel.dk Reviewed-by: Anuj Gupta anuj20.g@samsung.com Signed-off-by: Nitesh Shetty nj.shetty@samsung.com Cc: Al Viro viro@zeniv.linux.org.uk Cc: Christian Brauner brauner@kernel.org Cc: Keith Busch kbusch@kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- lib/iov_iter.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/lib/iov_iter.c b/lib/iov_iter.c index bc9391e55d57e..9ce83ab71bacd 100644 --- a/lib/iov_iter.c +++ b/lib/iov_iter.c @@ -820,7 +820,7 @@ static bool iov_iter_aligned_bvec(const struct iov_iter *i, unsigned addr_mask, size_t size = i->count;
do { - size_t len = bvec->bv_len; + size_t len = bvec->bv_len - skip;
if (len > size) len = size;