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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:
|
||
|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .clippy.toml | ||
| .cocciconfig | ||
| .editorconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .pylintrc | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.