Re: [PATCH 1/2] sched_getattr.2: update to include changed size semantics
From: Michael Kerrisk (man-pages) <hidden>
Date: 2020-09-30 10:51:45
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On 9/30/20 12:35 AM, Aleksa Sarai wrote:
Due to a userspace breakage, commit 1251201c0d34 ("sched/core: Fix
uclamp ABI bug, clean up and robustify sched_read_attr() ABI logic and
code") changed the semantics of sched_getattr(2) when the userspace
struct is smaller than the kernel struct. Now, any trailing non-zero
data in the kernel structure is ignored when copying to userspace. We
also document the original error code correctly (it was EFBIG not
E2BIG) in the BUGS section.Thanks, Aleksa. Patch applied. Cheers, Michael
quoted hunk ↗ jump to hunk
Ref: 1251201c0d34 ("sched/core: Fix uclamp ABI bug, clean up and robustify sched_read_attr() ABI logic and code") Signed-off-by: Aleksa Sarai <redacted> --- man2/sched_setattr.2 | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-)diff --git a/man2/sched_setattr.2 b/man2/sched_setattr.2 index 2592a761a086..da0972a6a86d 100644 --- a/man2/sched_setattr.2 +++ b/man2/sched_setattr.2@@ -286,10 +286,8 @@ structure, the additional bytes in the user-space structure are not touched. If the caller-provided structure is smaller than the kernel .I sched_attr -structure and the kernel needs to return values outside the provided space, -.BR sched_getattr () -fails with the error -.BR E2BIG . +structure, the kernel will silently not return any values which would be stored +outside the provided space. As with .BR sched_setattr (), these semantics allow for future extensibility of the interface.@@ -416,6 +414,16 @@ failed with the error instead of .BR E2BIG for the case described in ERRORS. +.PP +In Linux versions up to 5.3, +.BR sched_getattr () +failed with the error +.BR EFBIG +if the in-kernel +.IR sched_attr +structure was larger than the +.IR size +passed by user space. .\" In Linux versions up to up 3.15, .\" FIXME . patch from Peter Zijlstra pending .\" .BR sched_setattr ()
-- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/