kernel/linux.git/fs/select.c, branch v5.10.257

select: Fix unbalanced user_access_end()

2025-03-13T11:46:44+00:00

[ Upstream commit 344af27715ddbf357cf76978d674428b88f8e92d ] While working on implementing user access validation on powerpc I got the following warnings on a pmac32_defconfig build: CC fs/select.o fs/select.o: warning: objtool: sys_pselect6+0x1bc: redundant UACCESS disable fs/select.o: warning: objtool: sys_pselect6_time32+0x1bc: redundant UACCESS disable On powerpc/32s, user_read_access_begin/end() are no-ops, but the failure path has a user_access_end() instead of user_read_access_end() which means an access end without any prior access begin. Replace that user_access_end() by user_read_access_end(). Fixes: 7e71609f64ec ("pselect6() and friends: take handling the combined 6th/7th args into helper") Signed-off-by: Christophe Leroy Link: https://lore.kernel.org/r/a7139e28d767a13e667ee3c79599a8047222ef36.1736751221.git.christophe.leroy@csgroup.eu Signed-off-by: Christian Brauner Signed-off-by: Sasha Levin

fs/select: rework stack allocation hack for clang

2024-03-26T22:21:47+00:00

[ Upstream commit ddb9fd7a544088ed70eccbb9f85e9cc9952131c1 ] A while ago, we changed the way that select() and poll() preallocate a temporary buffer just under the size of the static warning limit of 1024 bytes, as clang was frequently going slightly above that limit. The warnings have recently returned and I took another look. As it turns out, clang is not actually inherently worse at reserving stack space, it just happens to inline do_select() into core_sys_select(), while gcc never inlines it. Annotate do_select() to never be inlined and in turn remove the special case for the allocation size. This should give the same behavior for both clang and gcc all the time and once more avoids those warnings. Fixes: ad312f95d41c ("fs/select: avoid clang stack usage warning") Signed-off-by: Arnd Bergmann Link: https://lore.kernel.org/r/20240216202352.2492798-1-arnd@kernel.org Reviewed-by: Kees Cook Reviewed-by: Andi Kleen Reviewed-by: Jan Kara Signed-off-by: Christian Brauner Signed-off-by: Sasha Levin

select: Fix indefinitely sleeping task in poll_schedule_timeout()

2022-01-29T09:26:11+00:00

commit 68514dacf2715d11b91ca50d88de047c086fea9c upstream. A task can end up indefinitely sleeping in do_select() -> poll_schedule_timeout() when the following race happens: TASK1 (thread1) TASK2 TASK1 (thread2) do_select() setup poll_wqueues table with 'fd' write data to 'fd' pollwake() table->triggered = 1 closes 'fd' thread1 is waiting for poll_schedule_timeout() - sees table->triggered table->triggered = 0 return -EINTR loop back in do_select() But at this point when TASK1 loops back, the fdget() in the setup of poll_wqueues fails. So now so we never find 'fd' is ready for reading and sleep in poll_schedule_timeout() indefinitely. Treat an fd that got closed as a fd on which some event happened. This makes sure cannot block indefinitely in do_select(). Another option would be to return -EBADF in this case but that has a potential of subtly breaking applications that excercise this behavior and it happens to work for them. So returning fd as active seems like a safer choice. Suggested-by: Linus Torvalds CC: stable@vger.kernel.org Signed-off-by: Jan Kara Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman

kernel, fs: Introduce and use set_restart_fn() and arch_set_restart_data()

2021-03-25T08:04:16+00:00

commit 5abbe51a526253b9f003e9a0a195638dc882d660 upstream. Preparation for fixing get_nr_restart_syscall() on X86 for COMPAT. Add a new helper which sets restart_block->fn and calls a dummy arch_set_restart_data() helper. Fixes: 609c19a385c8 ("x86/ptrace: Stop setting TS_COMPAT in ptrace code") Signed-off-by: Oleg Nesterov Signed-off-by: Thomas Gleixner Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20210201174641.GA17871@redhat.com Signed-off-by: Greg Kroah-Hartman

poll: fix performance regression due to out-of-line __put_user()

2021-01-19T17:27:27+00:00

[ Upstream commit ef0ba05538299f1391cbe097de36895bb36ecfe6 ] The kernel test robot reported a -5.8% performance regression on the "poll2" test of will-it-scale, and bisected it to commit d55564cfc222 ("x86: Make __put_user() generate an out-of-line call"). I didn't expect an out-of-line __put_user() to matter, because no normal core code should use that non-checking legacy version of user access any more. But I had overlooked the very odd poll() usage, which does a __put_user() to update the 'revents' values of the poll array. Now, Al Viro correctly points out that instead of updating just the 'revents' field, it would be much simpler to just copy the _whole_ pollfd entry, and then we could just use "copy_to_user()" on the whole array of entries, the same way we use "copy_from_user()" a few lines earlier to get the original values. But that is not what we've traditionally done, and I worry that threaded applications might be concurrently modifying the other fields of the pollfd array. So while Al's suggestion is simpler - and perhaps worth trying in the future - this instead keeps the "just update revents" model. To fix the performance regression, use the modern "unsafe_put_user()" instead of __put_user(), with the proper "user_write_access_begin()" guarding in place. This improves code generation enormously. Link: https://lore.kernel.org/lkml/20210107134723.GA28532@xsang-OptiPlex-9020/ Reported-by: kernel test robot Tested-by: Oliver Sang Cc: Al Viro Cc: David Laight Cc: Peter Zijlstra Signed-off-by: Linus Torvalds Signed-off-by: Sasha Levin

fs: Replace zero-length array with flexible-array member

2020-10-29T22:22:59+00:00

There is a regular need in the kernel to provide a way to declare having a dynamically sized set of trailing elements in a structure. Kernel code should always use “flexible array members”[1] for these cases. The older style of one-element or zero-length arrays should no longer be used[2]. [1] https://en.wikipedia.org/wiki/Flexible_array_member [2] https://www.kernel.org/doc/html/v5.9-rc1/process/deprecated.html#zero-length-and-one-element-arrays Signed-off-by: Gustavo A. R. Silva

pselect6() and friends: take handling the combined 6th/7th args into helper

2020-05-29T23:10:42+00:00

... and use unsafe_get_user(), while we are at it. Signed-off-by: Al Viro

y2038: syscalls: change remaining timeval to __kernel_old_timeval

2019-11-15T13:38:29+00:00

All of the remaining syscalls that pass a timeval (gettimeofday, utime, futimesat) can trivially be changed to pass a __kernel_old_timeval instead, which has a compatible layout, but avoids ambiguity with the timeval type in user space. Acked-by: Christian Brauner Acked-by: Rafael J. Wysocki Signed-off-by: Arnd Bergmann

fs/select.c: use struct_size() in kmalloc()

2019-07-17T02:23:25+00:00

One of the more common cases of allocation size calculations is finding the size of a structure that has a zero-sized array at the end, along with memory for some number of elements for that array. For example: struct foo { int stuff; struct boo entry[]; }; size = sizeof(struct foo) + count * sizeof(struct boo); instance = kmalloc(size, GFP_KERNEL); Instead of leaving these open-coded and prone to type mistakes, we can now use the new struct_size() helper: instance = kmalloc(struct_size(instance, entry, count), GFP_KERNEL); Also, notice that variable size is unnecessary, hence it is removed. This code was detected with the help of Coccinelle. Link: http://lkml.kernel.org/r/20190604164226.GA13823@embeddedor Signed-off-by: Gustavo A. R. Silva Reviewed-by: Andrew Morton Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

select: shift restore_saved_sigmask_unless() into poll_select_copy_remaining()

2019-07-17T02:23:24+00:00

Now that restore_saved_sigmask_unless() is always called with the same argument right before poll_select_copy_remaining() we can move it into poll_select_copy_remaining() and make it the only caller of restore() in fs/select.c. The patch also renames poll_select_copy_remaining(), poll_select_finish() looks better after this change. kern_select() doesn't use set_user_sigmask(), so in this case poll_select_finish() does restore_saved_sigmask_unless() "for no reason". But this won't hurt, and WARN_ON(!TIF_SIGPENDING) is still valid. Link: http://lkml.kernel.org/r/20190606140915.GC13440@redhat.com Signed-off-by: Oleg Nesterov Cc: Al Viro Cc: Arnd Bergmann Cc: David Laight Cc: Davidlohr Bueso Cc: Deepa Dinamani Cc: Eric W. Biederman Cc: Eric Wong Cc: Jason Baron Cc: Jens Axboe Cc: Thomas Gleixner Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds