Re: [RFC PATCH] mm/mempolicy: Fix memory leak in set_mempolicy_home_node system call
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From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: 2022-12-15 14:33:46
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On 2022-12-15 02:51, Michal Hocko wrote:
On Wed 14-12-22 17:21:10, Mathieu Desnoyers wrote:quoted
When encountering any vma in the range with policy other than MPOL_BIND or MPOL_PREFERRED_MANY, an error is returned without issuing a mpol_put on the policy just allocated with mpol_dup(). This allows arbitrary users to leak kernel memory. Fixes: c6018b4b2549 ("mm/mempolicy: add set_mempolicy_home_node syscall") Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: Aneesh Kumar K.V <redacted> Cc: Ben Widawsky <redacted> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Feng Tang <redacted> Cc: Michal Hocko <mhocko@kernel.org> Cc: Andrea Arcangeli <redacted> Cc: Mel Gorman <redacted> Cc: Mike Kravetz <redacted> Cc: Randy Dunlap <rdunlap@infradead.org> Cc: Vlastimil Babka <redacted> Cc: Andi Kleen <redacted> Cc: Dan Williams <redacted> Cc: Huang Ying <redacted> Cc: <redacted> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: stable@vger.kernel.org # 5.17+Acked-by: Michal Hocko <mhocko@suse.com> Thanks for catching this! Btw. looking at the code again it seems rather pointless to duplicate the policy just to throw it away anyway. A slightly bigger diff but this looks more reasonable to me. What do you think? I can also send it as a clean up on top of your fix.
I think it would be best if this comes as a cleanup on top of my fix. The diff is larger than the minimal change needed to fix the leak in stable branches. Your approach looks fine, except for the vma_policy(vma) -> old change already spotted by Aneesh. Thanks, Mathieu
quoted hunk ↗ jump to hunk
---diff --git a/mm/mempolicy.c b/mm/mempolicy.c index 61aa9aedb728..918cdc8a7f0c 100644 --- a/mm/mempolicy.c +++ b/mm/mempolicy.c@@ -1489,7 +1489,7 @@ SYSCALL_DEFINE4(set_mempolicy_home_node, unsigned long, start, unsigned long, le { struct mm_struct *mm = current->mm; struct vm_area_struct *vma; - struct mempolicy *new; + struct mempolicy *new. *old; unsigned long vmstart; unsigned long vmend; unsigned long end;@@ -1521,30 +1521,28 @@ SYSCALL_DEFINE4(set_mempolicy_home_node, unsigned long, start, unsigned long, le return 0; mmap_write_lock(mm); for_each_vma_range(vmi, vma, end) { - vmstart = max(start, vma->vm_start); - vmend = min(end, vma->vm_end); - new = mpol_dup(vma_policy(vma)); - if (IS_ERR(new)) { - err = PTR_ERR(new); - break; - } - /* - * Only update home node if there is an existing vma policy - */ - if (!new) - continue; - /* * If any vma in the range got policy other than MPOL_BIND * or MPOL_PREFERRED_MANY we return error. We don't reset * the home node for vmas we already updated before. */ - if (new->mode != MPOL_BIND && new->mode != MPOL_PREFERRED_MANY) { + old = vma_policy(vma); + if (!old) + continue; + if (old->mode != MPOL_BIND && old->mode != MPOL_PREFERRED_MANY) { err = -EOPNOTSUPP; break; } + new = mpol_dup(vma_policy(vma)); + if (IS_ERR(new)) { + err = PTR_ERR(new); + break; + } + new->home_node = home_node; + vmstart = max(start, vma->vm_start); + vmend = min(end, vma->vm_end); err = mbind_range(mm, vmstart, vmend, new); mpol_put(new); if (err)
-- Mathieu Desnoyers EfficiOS Inc. https://www.efficios.com