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| author | Michal Koutný <mkoutny@suse.com> | 2019-05-31 22:30:19 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2019-06-01 15:51:31 -0700 |
| commit | bc81426f5beef7da863d3365bc9d45e820448745 (patch) | |
| tree | c26cfabbc7b48e47b65ea33060067dd7b00567c1 /kernel/sys.c | |
| parent | 11bbd8b416f8abf40900dc5041152892f873d915 (diff) | |
| download | lwn-bc81426f5beef7da863d3365bc9d45e820448745.tar.gz lwn-bc81426f5beef7da863d3365bc9d45e820448745.zip | |
prctl_set_mm: downgrade mmap_sem to read lock
The commit a3b609ef9f8b ("proc read mm's {arg,env}_{start,end} with mmap
semaphore taken.") added synchronization of reading argument/environment
boundaries under mmap_sem. Later commit 88aa7cc688d4 ("mm: introduce
arg_lock to protect arg_start|end and env_start|end in mm_struct") avoided
the coarse use of mmap_sem in similar situations. But there still
remained two places that (mis)use mmap_sem.
get_cmdline should also use arg_lock instead of mmap_sem when it reads the
boundaries.
The second place that should use arg_lock is in prctl_set_mm. By
protecting the boundaries fields with the arg_lock, we can downgrade
mmap_sem to reader lock (analogous to what we already do in
prctl_set_mm_map).
[akpm@linux-foundation.org: coding style fixes]
Link: http://lkml.kernel.org/r/20190502125203.24014-3-mkoutny@suse.com
Fixes: 88aa7cc688d4 ("mm: introduce arg_lock to protect arg_start|end and env_start|end in mm_struct")
Signed-off-by: Michal Koutný <mkoutny@suse.com>
Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com>
Co-developed-by: Laurent Dufour <ldufour@linux.ibm.com>
Reviewed-by: Cyrill Gorcunov <gorcunov@gmail.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Yang Shi <yang.shi@linux.alibaba.com>
Cc: Mateusz Guzik <mguzik@redhat.com>
Cc: Kirill Tkhai <ktkhai@virtuozzo.com>
Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel/sys.c')
| -rw-r--r-- | kernel/sys.c | 11 |
1 files changed, 9 insertions, 2 deletions
diff --git a/kernel/sys.c b/kernel/sys.c index 775bf8d18d03..2969304c29fe 100644 --- a/kernel/sys.c +++ b/kernel/sys.c @@ -2127,9 +2127,15 @@ static int prctl_set_mm(int opt, unsigned long addr, error = -EINVAL; - down_write(&mm->mmap_sem); + /* + * arg_lock protects concurent updates of arg boundaries, we need + * mmap_sem for a) concurrent sys_brk, b) finding VMA for addr + * validation. + */ + down_read(&mm->mmap_sem); vma = find_vma(mm, addr); + spin_lock(&mm->arg_lock); prctl_map.start_code = mm->start_code; prctl_map.end_code = mm->end_code; prctl_map.start_data = mm->start_data; @@ -2217,7 +2223,8 @@ static int prctl_set_mm(int opt, unsigned long addr, error = 0; out: - up_write(&mm->mmap_sem); + spin_unlock(&mm->arg_lock); + up_read(&mm->mmap_sem); return error; } |