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author | David Rientjes <rientjes@google.com> | 2012-10-17 02:31:23 +0200 |
---|---|---|
committer | Linus Torvalds <torvalds@linux-foundation.org> | 2012-10-17 03:00:50 +0200 |
commit | 32f8516a8c733d281faa9f6666b509035246505c (patch) | |
tree | 31e40b8d5c96dec8a3e6f8adfb3db992718fecc1 /fs/proc/task_mmu.c | |
parent | thermal, cpufreq: Fix build when CPU_FREQ_TABLE isn't configured (diff) | |
download | linux-32f8516a8c733d281faa9f6666b509035246505c.tar.xz linux-32f8516a8c733d281faa9f6666b509035246505c.zip |
mm, mempolicy: fix printing stack contents in numa_maps
When reading /proc/pid/numa_maps, it's possible to return the contents of
the stack where the mempolicy string should be printed if the policy gets
freed from beneath us.
This happens because mpol_to_str() may return an error the
stack-allocated buffer is then printed without ever being stored.
There are two possible error conditions in mpol_to_str():
- if the buffer allocated is insufficient for the string to be stored,
and
- if the mempolicy has an invalid mode.
The first error condition is not triggered in any of the callers to
mpol_to_str(): at least 50 bytes is always allocated on the stack and this
is sufficient for the string to be written. A future patch should convert
this into BUILD_BUG_ON() since we know the maximum strlen possible, but
that's not -rc material.
The second error condition is possible if a race occurs in dropping a
reference to a task's mempolicy causing it to be freed during the read().
The slab poison value is then used for the mode and mpol_to_str() returns
-EINVAL.
This race is only possible because get_vma_policy() believes that
mm->mmap_sem protects task->mempolicy, which isn't true. The exit path
does not hold mm->mmap_sem when dropping the reference or setting
task->mempolicy to NULL: it uses task_lock(task) instead.
Thus, it's required for the caller of a task mempolicy to hold
task_lock(task) while grabbing the mempolicy and reading it. Callers with
a vma policy store their mempolicy earlier and can simply increment the
reference count so it's guaranteed not to be freed.
Reported-by: Dave Jones <davej@redhat.com>
Signed-off-by: David Rientjes <rientjes@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'fs/proc/task_mmu.c')
-rw-r--r-- | fs/proc/task_mmu.c | 7 |
1 files changed, 5 insertions, 2 deletions
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c index 79827ce03e3b..14df8806ff29 100644 --- a/fs/proc/task_mmu.c +++ b/fs/proc/task_mmu.c @@ -1158,6 +1158,7 @@ static int show_numa_map(struct seq_file *m, void *v, int is_pid) struct vm_area_struct *vma = v; struct numa_maps *md = &numa_priv->md; struct file *file = vma->vm_file; + struct task_struct *task = proc_priv->task; struct mm_struct *mm = vma->vm_mm; struct mm_walk walk = {}; struct mempolicy *pol; @@ -1177,9 +1178,11 @@ static int show_numa_map(struct seq_file *m, void *v, int is_pid) walk.private = md; walk.mm = mm; - pol = get_vma_policy(proc_priv->task, vma, vma->vm_start); + task_lock(task); + pol = get_vma_policy(task, vma, vma->vm_start); mpol_to_str(buffer, sizeof(buffer), pol, 0); mpol_cond_put(pol); + task_unlock(task); seq_printf(m, "%08lx %s", vma->vm_start, buffer); @@ -1189,7 +1192,7 @@ static int show_numa_map(struct seq_file *m, void *v, int is_pid) } else if (vma->vm_start <= mm->brk && vma->vm_end >= mm->start_brk) { seq_printf(m, " heap"); } else { - pid_t tid = vm_is_stack(proc_priv->task, vma, is_pid); + pid_t tid = vm_is_stack(task, vma, is_pid); if (tid != 0) { /* * Thread stack in /proc/PID/task/TID/maps or |