diff options
author | Oleg Nesterov <oleg@redhat.com> | 2012-01-31 17:15:11 +0100 |
---|---|---|
committer | Linus Torvalds <torvalds@linux-foundation.org> | 2012-02-01 14:39:01 -0800 |
commit | 6d08f2c7139790c268820a2e590795cb8333181a (patch) | |
tree | 78b2773b8ca6949f9561af641908e4086ba193cb | |
parent | 572d34b946bae070debd42db1143034d9687e13f (diff) |
proc: make sure mem_open() doesn't pin the target's memory
Once /proc/pid/mem is opened, the memory can't be released until
mem_release() even if its owner exits.
Change mem_open() to do atomic_inc(mm_count) + mmput(), this only
pins mm_struct. Change mem_rw() to do atomic_inc_not_zero(mm_count)
before access_remote_vm(), this verifies that this mm is still alive.
I am not sure what should mem_rw() return if atomic_inc_not_zero()
fails. With this patch it returns zero to match the "mm == NULL" case,
may be it should return -EINVAL like it did before e268337d.
Perhaps it makes sense to add the additional fatal_signal_pending()
check into the main loop, to ensure we do not hold this memory if
the target task was oom-killed.
Cc: stable@kernel.org
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r-- | fs/proc/base.c | 14 |
1 files changed, 13 insertions, 1 deletions
diff --git a/fs/proc/base.c b/fs/proc/base.c index be190904168..d9512bd03e6 100644 --- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -711,6 +711,13 @@ static int mem_open(struct inode* inode, struct file* file) if (IS_ERR(mm)) return PTR_ERR(mm); + if (mm) { + /* ensure this mm_struct can't be freed */ + atomic_inc(&mm->mm_count); + /* but do not pin its memory */ + mmput(mm); + } + /* OK to pass negative loff_t, we can catch out-of-range */ file->f_mode |= FMODE_UNSIGNED_OFFSET; file->private_data = mm; @@ -734,6 +741,9 @@ static ssize_t mem_rw(struct file *file, char __user *buf, return -ENOMEM; copied = 0; + if (!atomic_inc_not_zero(&mm->mm_users)) + goto free; + while (count > 0) { int this_len = min_t(int, count, PAGE_SIZE); @@ -761,6 +771,8 @@ static ssize_t mem_rw(struct file *file, char __user *buf, } *ppos = addr; + mmput(mm); +free: free_page((unsigned long) page); return copied; } @@ -797,7 +809,7 @@ static int mem_release(struct inode *inode, struct file *file) { struct mm_struct *mm = file->private_data; if (mm) - mmput(mm); + mmdrop(mm); return 0; } |