This is a note to let you know that I've just added the patch titled mm/madvise: replace ptrace attach requirement for process_madvise to the 5.11-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: mm-madvise-replace-ptrace-attach-requirement-for-process_madvise.patch and it can be found in the queue-5.11 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 96cfe2c0fd23ea7c2368d14f769d287e7ae1082e Mon Sep 17 00:00:00 2001 From: Suren Baghdasaryan <surenb@xxxxxxxxxx> Date: Fri, 12 Mar 2021 21:08:06 -0800 Subject: mm/madvise: replace ptrace attach requirement for process_madvise From: Suren Baghdasaryan <surenb@xxxxxxxxxx> commit 96cfe2c0fd23ea7c2368d14f769d287e7ae1082e upstream. process_madvise currently requires ptrace attach capability. PTRACE_MODE_ATTACH gives one process complete control over another process. It effectively removes the security boundary between the two processes (in one direction). Granting ptrace attach capability even to a system process is considered dangerous since it creates an attack surface. This severely limits the usage of this API. The operations process_madvise can perform do not affect the correctness of the operation of the target process; they only affect where the data is physically located (and therefore, how fast it can be accessed). What we want is the ability for one process to influence another process in order to optimize performance across the entire system while leaving the security boundary intact. Replace PTRACE_MODE_ATTACH with a combination of PTRACE_MODE_READ and CAP_SYS_NICE. PTRACE_MODE_READ to prevent leaking ASLR metadata and CAP_SYS_NICE for influencing process performance. Link: https://lkml.kernel.org/r/20210303185807.2160264-1-surenb@xxxxxxxxxx Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx> Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> Acked-by: Minchan Kim <minchan@xxxxxxxxxx> Acked-by: David Rientjes <rientjes@xxxxxxxxxx> Cc: Jann Horn <jannh@xxxxxxxxxx> Cc: Jeff Vander Stoep <jeffv@xxxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxx> Cc: Shakeel Butt <shakeelb@xxxxxxxxxx> Cc: Tim Murray <timmurray@xxxxxxxxxx> Cc: Florian Weimer <fweimer@xxxxxxxxxx> Cc: Oleg Nesterov <oleg@xxxxxxxxxx> Cc: James Morris <jmorris@xxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> [5.10+] Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- mm/madvise.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) --- a/mm/madvise.c +++ b/mm/madvise.c @@ -1197,12 +1197,22 @@ SYSCALL_DEFINE5(process_madvise, int, pi goto release_task; } - mm = mm_access(task, PTRACE_MODE_ATTACH_FSCREDS); + /* Require PTRACE_MODE_READ to avoid leaking ASLR metadata. */ + mm = mm_access(task, PTRACE_MODE_READ_FSCREDS); if (IS_ERR_OR_NULL(mm)) { ret = IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH; goto release_task; } + /* + * Require CAP_SYS_NICE for influencing process performance. Note that + * only non-destructive hints are currently supported. + */ + if (!capable(CAP_SYS_NICE)) { + ret = -EPERM; + goto release_mm; + } + total_len = iov_iter_count(&iter); while (iov_iter_count(&iter)) { @@ -1217,6 +1227,7 @@ SYSCALL_DEFINE5(process_madvise, int, pi if (ret == 0) ret = total_len - iov_iter_count(&iter); +release_mm: mmput(mm); release_task: put_task_struct(task); Patches currently in stable-queue which might be from surenb@xxxxxxxxxx are queue-5.11/mm-madvise-replace-ptrace-attach-requirement-for-process_madvise.patch