While doing this, I detected some anomalies in the existing code:
mm/kfence/kfence_test.c:
- The last call to scnprintf() did increment 'cur', but it's
unused after that, so it was dead code. I've removed the dead
code in this patch.
- 'end' is calculated as
end = &expect[0][sizeof(expect[0] - 1)];
However, the '-1' doesn't seem to be necessary. When passing
$2 to scnprintf(), the size was specified as 'end - cur'.
And scnprintf() --just like snprintf(3)--, won't write more
than $2 bytes (including the null byte). That means that
scnprintf() wouldn't write more than
&expect[0][sizeof(expect[0]) - 1] - expect[0]
which simplifies to
sizeof(expect[0]) - 1
bytes. But we have sizeof(expect[0]) bytes available, so
we're wasting one byte entirely. This is a benign off-by-one
bug. The two occurrences of this bug will be fixed in a
following patch in this series.
mm/kmsan/kmsan_test.c:
The same benign off-by-one bug calculating the remaining size.
mm/mempolicy.c:
This file uses the 'p += snprintf()' anti-pattern. That will
overflow the pointer on truncation, which has undefined
behavior. Using sprintf_end(), this bug is fixed.
As in the previous file, here there was also dead code in the
last scnprintf() call, by incrementing a pointer that is not
used after the call. I've removed the dead code.
mm/page_owner.c:
Within print_page_owner(), there are some calls to scnprintf(),
which do report truncation. And then there are other calls to
snprintf(), where we handle errors (there are two 'goto err').
I've kept the existing error handling, as I trust it's there for
a good reason (i.e., we may want to avoid calling
print_page_owner_memcg() if we truncated before). Please review
if this amount of error handling is the right one, or if we want
to add or remove some. For sprintf_end(), a single test for
null after the last call is enough to detect truncation.
mm/slub.c:
Again, the 'p += snprintf()' anti-pattern. This is UB, and by
using sprintf_end() we've fixed the bug.
Cc: Kees Cook <k...@kernel.org>
Cc: Christopher Bazley <chris.bazley.w...@gmail.com>
Cc: Sven Schnelle <sv...@linux.ibm.com>
Cc: Marco Elver <el...@google.com>
Cc: Heiko Carstens <h...@linux.ibm.com>
Cc: Tvrtko Ursulin <tvrtko.ursu...@igalia.com>
Cc: Andrew Morton <a...@linux-foundation.org>
Cc: Linus Torvalds <torva...@linux-foundation.org>
Cc: David Rientjes <rient...@google.com>
Cc: Christophe JAILLET <christophe.jail...@wanadoo.fr>
Cc: Hyeonggon Yoo <42.hye...@gmail.com>
Cc: Chao Yu <chao...@oppo.com>
Cc: Vlastimil Babka <vba...@suse.cz>
Cc: Rasmus Villemoes <li...@rasmusvillemoes.dk>
Cc: Michal Hocko <mho...@suse.com>
Cc: Al Viro <v...@zeniv.linux.org.uk>
Signed-off-by: Alejandro Colomar <a...@kernel.org>
---
mm/kfence/kfence_test.c | 24 ++++++++++++------------
mm/kmsan/kmsan_test.c | 4 ++--
mm/mempolicy.c | 18 +++++++++---------
mm/page_owner.c | 32 +++++++++++++++++---------------
mm/slub.c | 5 +++--
5 files changed, 43 insertions(+), 40 deletions(-)
diff --git a/mm/kfence/kfence_test.c b/mm/kfence/kfence_test.c
index 00034e37bc9f..bae382eca4ab 100644
--- a/mm/kfence/kfence_test.c
+++ b/mm/kfence/kfence_test.c
@@ -113,26 +113,26 @@ static bool report_matches(const struct expect_report *r)
end = &expect[0][sizeof(expect[0]) - 1];
switch (r->type) {
case KFENCE_ERROR_OOB:
- cur += scnprintf(cur, end - cur, "BUG: KFENCE: out-of-bounds
%s",
+ cur = sprintf_end(cur, end, "BUG: KFENCE: out-of-bounds %s",
get_access_type(r));
break;
case KFENCE_ERROR_UAF:
- cur += scnprintf(cur, end - cur, "BUG: KFENCE: use-after-free
%s",
+ cur = sprintf_end(cur, end, "BUG: KFENCE: use-after-free %s",
get_access_type(r));
break;
case KFENCE_ERROR_CORRUPTION:
- cur += scnprintf(cur, end - cur, "BUG: KFENCE: memory
corruption");
+ cur = sprintf_end(cur, end, "BUG: KFENCE: memory corruption");
break;
case KFENCE_ERROR_INVALID:
- cur += scnprintf(cur, end - cur, "BUG: KFENCE: invalid %s",
+ cur = sprintf_end(cur, end, "BUG: KFENCE: invalid %s",
get_access_type(r));
break;
case KFENCE_ERROR_INVALID_FREE:
- cur += scnprintf(cur, end - cur, "BUG: KFENCE: invalid free");
+ cur = sprintf_end(cur, end, "BUG: KFENCE: invalid free");
break;
}
- scnprintf(cur, end - cur, " in %pS", r->fn);
+ sprintf_end(cur, end, " in %pS", r->fn);
/* The exact offset won't match, remove it; also strip module name. */
cur = strchr(expect[0], '+');
if (cur)
@@ -144,26 +144,26 @@ static bool report_matches(const struct expect_report *r)
switch (r->type) {
case KFENCE_ERROR_OOB:
- cur += scnprintf(cur, end - cur, "Out-of-bounds %s at",
get_access_type(r));
+ cur = sprintf_end(cur, end, "Out-of-bounds %s at",
get_access_type(r));
addr = arch_kfence_test_address(addr);
break;
case KFENCE_ERROR_UAF:
- cur += scnprintf(cur, end - cur, "Use-after-free %s at",
get_access_type(r));
+ cur = sprintf_end(cur, end, "Use-after-free %s at",
get_access_type(r));
addr = arch_kfence_test_address(addr);
break;
case KFENCE_ERROR_CORRUPTION:
- cur += scnprintf(cur, end - cur, "Corrupted memory at");
+ cur = sprintf_end(cur, end, "Corrupted memory at");
break;
case KFENCE_ERROR_INVALID:
- cur += scnprintf(cur, end - cur, "Invalid %s at",
get_access_type(r));
+ cur = sprintf_end(cur, end, "Invalid %s at",
get_access_type(r));
addr = arch_kfence_test_address(addr);
break;
case KFENCE_ERROR_INVALID_FREE:
- cur += scnprintf(cur, end - cur, "Invalid free of");
+ cur = sprintf_end(cur, end, "Invalid free of");
break;
}
- cur += scnprintf(cur, end - cur, " 0x%p", (void *)addr);
+ sprintf_end(cur, end, " 0x%p", (void *)addr);
spin_lock_irqsave(&observed.lock, flags);
if (!report_available())
diff --git a/mm/kmsan/kmsan_test.c b/mm/kmsan/kmsan_test.c
index 9733a22c46c1..e48ca1972ff3 100644
--- a/mm/kmsan/kmsan_test.c
+++ b/mm/kmsan/kmsan_test.c
@@ -107,9 +107,9 @@ static bool report_matches(const struct expect_report *r)
cur = expected_header;
end = &expected_header[sizeof(expected_header) - 1];
- cur += scnprintf(cur, end - cur, "BUG: KMSAN: %s", r->error_type);
+ cur = sprintf_end(cur, end, "BUG: KMSAN: %s", r->error_type);
- scnprintf(cur, end - cur, " in %s", r->symbol);
+ sprintf_end(cur, end, " in %s", r->symbol);
/* The exact offset won't match, remove it; also strip module name. */
cur = strchr(expected_header, '+');
if (cur)
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index b28a1e6ae096..6beb2710f97c 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -3359,6 +3359,7 @@ int mpol_parse_str(char *str, struct mempolicy **mpol)
void mpol_to_str(char *buffer, int maxlen, struct mempolicy *pol)
{
char *p = buffer;
+ char *e = buffer + maxlen;
nodemask_t nodes = NODE_MASK_NONE;
unsigned short mode = MPOL_DEFAULT;
unsigned short flags = 0;
@@ -3384,33 +3385,32 @@ void mpol_to_str(char *buffer, int maxlen, struct
mempolicy *pol)
break;
default:
WARN_ON_ONCE(1);
- snprintf(p, maxlen, "unknown");
+ sprintf_end(p, e, "unknown");
return;
}
- p += snprintf(p, maxlen, "%s", policy_modes[mode]);
+ p = sprintf_end(p, e, "%s", policy_modes[mode]);
if (flags & MPOL_MODE_FLAGS) {
- p += snprintf(p, buffer + maxlen - p, "=");
+ p = sprintf_end(p, e, "=");
/*
* Static and relative are mutually exclusive.
*/
if (flags & MPOL_F_STATIC_NODES)
- p += snprintf(p, buffer + maxlen - p, "static");
+ p = sprintf_end(p, e, "static");
else if (flags & MPOL_F_RELATIVE_NODES)
- p += snprintf(p, buffer + maxlen - p, "relative");
+ p = sprintf_end(p, e, "relative");
if (flags & MPOL_F_NUMA_BALANCING) {
if (!is_power_of_2(flags & MPOL_MODE_FLAGS))
- p += snprintf(p, buffer + maxlen - p, "|");
- p += snprintf(p, buffer + maxlen - p, "balancing");
+ p = sprintf_end(p, e, "|");
+ p = sprintf_end(p, e, "balancing");
}
}
if (!nodes_empty(nodes))
- p += scnprintf(p, buffer + maxlen - p, ":%*pbl",
- nodemask_pr_args(&nodes));
+ sprintf_end(p, e, ":%*pbl", nodemask_pr_args(&nodes));
}
#ifdef CONFIG_SYSFS
diff --git a/mm/page_owner.c b/mm/page_owner.c
index cc4a6916eec6..c00b3be01540 100644
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -496,7 +496,7 @@ void pagetypeinfo_showmixedcount_print(struct seq_file *m,
/*
* Looking for memcg information and print it out
*/
-static inline int print_page_owner_memcg(char *kbuf, size_t count, int ret,
+static inline char *print_page_owner_memcg(char *p, const char end[0],
struct page *page)
{
#ifdef CONFIG_MEMCG
@@ -511,8 +511,7 @@ static inline int print_page_owner_memcg(char *kbuf, size_t
count, int ret,
goto out_unlock;
if (memcg_data & MEMCG_DATA_OBJEXTS)
- ret += scnprintf(kbuf + ret, count - ret,
- "Slab cache page\n");
+ p = sprintf_end(p, end, "Slab cache page\n");
memcg = page_memcg_check(page);
if (!memcg)
@@ -520,7 +519,7 @@ static inline int print_page_owner_memcg(char *kbuf, size_t
count, int ret,
online = (memcg->css.flags & CSS_ONLINE);
cgroup_name(memcg->css.cgroup, name, sizeof(name));
- ret += scnprintf(kbuf + ret, count - ret,
+ p = sprintf_end(p, end,
"Charged %sto %smemcg %s\n",
PageMemcgKmem(page) ? "(via objcg) " : "",
online ? "" : "offline ",
@@ -529,7 +528,7 @@ static inline int print_page_owner_memcg(char *kbuf, size_t
count, int ret,
rcu_read_unlock();
#endif /* CONFIG_MEMCG */
- return ret;
+ return p;
}
static ssize_t
@@ -538,14 +537,16 @@ print_page_owner(char __user *buf, size_t count, unsigned
long pfn,
depot_stack_handle_t handle)
{
int ret, pageblock_mt, page_mt;
- char *kbuf;
+ char *kbuf, *p, *e;
count = min_t(size_t, count, PAGE_SIZE);
kbuf = kmalloc(count, GFP_KERNEL);
if (!kbuf)
return -ENOMEM;
- ret = scnprintf(kbuf, count,
+ p = kbuf;
+ e = kbuf + count;
+ p = sprintf_end(p, e,
"Page allocated via order %u, mask %#x(%pGg), pid %d,
tgid %d (%s), ts %llu ns\n",
page_owner->order, page_owner->gfp_mask,
&page_owner->gfp_mask, page_owner->pid,
@@ -555,7 +556,7 @@ print_page_owner(char __user *buf, size_t count, unsigned
long pfn,
/* Print information relevant to grouping pages by mobility */
pageblock_mt = get_pageblock_migratetype(page);
page_mt = gfp_migratetype(page_owner->gfp_mask);
- ret += scnprintf(kbuf + ret, count - ret,
+ p = sprintf_end(p, e,
"PFN 0x%lx type %s Block %lu type %s Flags %pGp\n",
pfn,
migratetype_names[page_mt],
@@ -563,22 +564,23 @@ print_page_owner(char __user *buf, size_t count, unsigned
long pfn,
migratetype_names[pageblock_mt],
&page->flags);
- ret += stack_depot_snprint(handle, kbuf + ret, count - ret, 0);
- if (ret >= count)
- goto err;
+ p = stack_depot_sprint_end(handle, p, e, 0);
+ if (p == NULL)
+ goto err; // XXX: Should we remove this error handling?
if (page_owner->last_migrate_reason != -1) {
- ret += scnprintf(kbuf + ret, count - ret,
+ p = sprintf_end(p, e,
"Page has been migrated, last migrate reason: %s\n",
migrate_reason_names[page_owner->last_migrate_reason]);
}
- ret = print_page_owner_memcg(kbuf, count, ret, page);
+ p = print_page_owner_memcg(p, e, page);
- ret += snprintf(kbuf + ret, count - ret, "\n");
- if (ret >= count)
+ p = sprintf_end(p, e, "\n");
+ if (p == NULL)
goto err;
+ ret = p - kbuf;
if (copy_to_user(buf, kbuf, ret))
ret = -EFAULT;
diff --git a/mm/slub.c b/mm/slub.c
index be8b09e09d30..dcc857676857 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -7451,6 +7451,7 @@ static char *create_unique_id(struct kmem_cache *s)
{
char *name = kmalloc(ID_STR_LENGTH, GFP_KERNEL);
char *p = name;
+ char *e = name + ID_STR_LENGTH;
if (!name)
return ERR_PTR(-ENOMEM);
@@ -7475,9 +7476,9 @@ static char *create_unique_id(struct kmem_cache *s)
*p++ = 'A';
if (p != name + 1)
*p++ = '-';
- p += snprintf(p, ID_STR_LENGTH - (p - name), "%07u", s->size);
+ p = sprintf_end(p, e, "%07u", s->size);
- if (WARN_ON(p > name + ID_STR_LENGTH - 1)) {
+ if (WARN_ON(p == NULL)) {
kfree(name);
return ERR_PTR(-EINVAL);
}
--
2.50.0
