From f2a07f40dbc603c15f8b06e6ec7f768af67b424f Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Wed, 2 Jan 2013 02:01:33 -0800 Subject: [PATCH] tmpfs mempolicy: fix /proc/mounts corrupting memory Recently I suggested using "mount -o remount,mpol=local /tmp" in NUMA mempolicy testing. Very nasty. Reading /proc/mounts, /proc/pid/mounts or /proc/pid/mountinfo may then corrupt one bit of kernel memory, often in a page table (causing "Bad swap" or "Bad page map" warning or "Bad pagetable" oops), sometimes in a vm_area_struct or rbnode or somewhere worse. "mpol=prefer" and "mpol=prefer:Node" are equally toxic. Recent NUMA enhancements are not to blame: this dates back to 2.6.35, when commit e17f74af351c "mempolicy: don't call mpol_set_nodemask() when no_context" skipped mpol_parse_str()'s call to mpol_set_nodemask(), which used to initialize v.preferred_node, or set MPOL_F_LOCAL in flags. With slab poisoning, you can then rely on mpol_to_str() to set the bit for node 0x6b6b, probably in the next page above the caller's stack. mpol_parse_str() is only called from shmem_parse_options(): no_context is always true, so call it unused for now, and remove !no_context code. Set v.nodes or v.preferred_node or MPOL_F_LOCAL as mpol_to_str() might expect. Then mpol_to_str() can ignore its no_context argument also, the mpol being appropriately initialized whether contextualized or not. Rename its no_context unused too, and let subsequent patch remove them (that's not needed for stable backporting, which would involve rejects). I don't understand why MPOL_LOCAL is described as a pseudo-policy: it's a reasonable policy which suffers from a confusing implementation in terms of MPOL_PREFERRED with MPOL_F_LOCAL. I believe this would be much more robust if MPOL_LOCAL were recognized in switch statements throughout, MPOL_F_LOCAL deleted, and MPOL_PREFERRED use the (possibly empty) nodes mask like everyone else, instead of its preferred_node variant (I presume an optimization from the days before MPOL_LOCAL). But that would take me too long to get right and fully tested. Signed-off-by: Hugh Dickins Cc: stable@vger.kernel.org Signed-off-by: Linus Torvalds --- mm/mempolicy.c | 64 ++++++++++++++++++++++++---------------------------------- 1 file changed, 26 insertions(+), 38 deletions(-) diff --git a/mm/mempolicy.c b/mm/mempolicy.c index d1b315e..02c914c 100644 --- a/mm/mempolicy.c +++ b/mm/mempolicy.c @@ -2595,8 +2595,7 @@ void numa_default_policy(void) */ /* - * "local" is pseudo-policy: MPOL_PREFERRED with MPOL_F_LOCAL flag - * Used only for mpol_parse_str() and mpol_to_str() + * "local" is implemented internally by MPOL_PREFERRED with MPOL_F_LOCAL flag. */ static const char * const policy_modes[] = { @@ -2610,28 +2609,21 @@ static const char * const policy_modes[] = #ifdef CONFIG_TMPFS /** - * mpol_parse_str - parse string to mempolicy + * mpol_parse_str - parse string to mempolicy, for tmpfs mpol mount option. * @str: string containing mempolicy to parse * @mpol: pointer to struct mempolicy pointer, returned on success. - * @no_context: flag whether to "contextualize" the mempolicy + * @unused: redundant argument, to be removed later. * * Format of input: * [=][:] * - * if @no_context is true, save the input nodemask in w.user_nodemask in - * the returned mempolicy. This will be used to "clone" the mempolicy in - * a specific context [cpuset] at a later time. Used to parse tmpfs mpol - * mount option. Note that if 'static' or 'relative' mode flags were - * specified, the input nodemask will already have been saved. Saving - * it again is redundant, but safe. - * * On success, returns 0, else 1 */ -int mpol_parse_str(char *str, struct mempolicy **mpol, int no_context) +int mpol_parse_str(char *str, struct mempolicy **mpol, int unused) { struct mempolicy *new = NULL; unsigned short mode; - unsigned short uninitialized_var(mode_flags); + unsigned short mode_flags; nodemask_t nodes; char *nodelist = strchr(str, ':'); char *flags = strchr(str, '='); @@ -2719,24 +2711,23 @@ int mpol_parse_str(char *str, struct mempolicy **mpol, int no_context) if (IS_ERR(new)) goto out; - if (no_context) { - /* save for contextualization */ - new->w.user_nodemask = nodes; - } else { - int ret; - NODEMASK_SCRATCH(scratch); - if (scratch) { - task_lock(current); - ret = mpol_set_nodemask(new, &nodes, scratch); - task_unlock(current); - } else - ret = -ENOMEM; - NODEMASK_SCRATCH_FREE(scratch); - if (ret) { - mpol_put(new); - goto out; - } - } + /* + * Save nodes for mpol_to_str() to show the tmpfs mount options + * for /proc/mounts, /proc/pid/mounts and /proc/pid/mountinfo. + */ + if (mode != MPOL_PREFERRED) + new->v.nodes = nodes; + else if (nodelist) + new->v.preferred_node = first_node(nodes); + else + new->flags |= MPOL_F_LOCAL; + + /* + * Save nodes for contextualization: this will be used to "clone" + * the mempolicy in a specific context [cpuset] at a later time. + */ + new->w.user_nodemask = nodes; + err = 0; out: @@ -2756,13 +2747,13 @@ out: * @buffer: to contain formatted mempolicy string * @maxlen: length of @buffer * @pol: pointer to mempolicy to be formatted - * @no_context: "context free" mempolicy - use nodemask in w.user_nodemask + * @unused: redundant argument, to be removed later. * * Convert a mempolicy into a string. * Returns the number of characters in buffer (if positive) * or an error (negative) */ -int mpol_to_str(char *buffer, int maxlen, struct mempolicy *pol, int no_context) +int mpol_to_str(char *buffer, int maxlen, struct mempolicy *pol, int unused) { char *p = buffer; int l; @@ -2788,7 +2779,7 @@ int mpol_to_str(char *buffer, int maxlen, struct mempolicy *pol, int no_context) case MPOL_PREFERRED: nodes_clear(nodes); if (flags & MPOL_F_LOCAL) - mode = MPOL_LOCAL; /* pseudo-policy */ + mode = MPOL_LOCAL; else node_set(pol->v.preferred_node, nodes); break; @@ -2796,10 +2787,7 @@ int mpol_to_str(char *buffer, int maxlen, struct mempolicy *pol, int no_context) case MPOL_BIND: /* Fall through */ case MPOL_INTERLEAVE: - if (no_context) - nodes = pol->w.user_nodemask; - else - nodes = pol->v.nodes; + nodes = pol->v.nodes; break; default: -- 2.7.4