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authorMichal Koutný <mkoutny@suse.com>2019-05-31 22:30:19 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2019-06-01 15:51:31 -0700
commitbc81426f5beef7da863d3365bc9d45e820448745 (patch)
treec26cfabbc7b48e47b65ea33060067dd7b00567c1 /kernel/sys.c
parent11bbd8b416f8abf40900dc5041152892f873d915 (diff)
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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.c11
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;
}