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32f8516a8c
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> |
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| .. | ||
| array.c | ||
| base.c | ||
| cmdline.c | ||
| consoles.c | ||
| cpuinfo.c | ||
| devices.c | ||
| fd.c | ||
| fd.h | ||
| generic.c | ||
| inode.c | ||
| internal.h | ||
| interrupts.c | ||
| Kconfig | ||
| kcore.c | ||
| kmsg.c | ||
| loadavg.c | ||
| Makefile | ||
| meminfo.c | ||
| mmu.c | ||
| namespaces.c | ||
| nommu.c | ||
| page.c | ||
| proc_devtree.c | ||
| proc_net.c | ||
| proc_sysctl.c | ||
| proc_tty.c | ||
| root.c | ||
| softirqs.c | ||
| stat.c | ||
| task_mmu.c | ||
| task_nommu.c | ||
| uptime.c | ||
| version.c | ||
| vmcore.c | ||