[PATCH v2 1/3] mm/slub: Clarify verification reporting

Kees Cook
2020-10-09T19:54:22Z

Instead of repeating "Redzone" and "Poison", clarify which sides of
those zones got tripped. Additionally fix column alignment in the
trailer.

Before:

BUG test (Tainted: G B ): Redzone overwritten
...
Redzone (____ptrval____): bb bb bb bb bb bb bb bb ........
Object (____ptrval____): f6 f4 a5 40 1d e8 ...@..
Redzone (____ptrval____): 1a aa ..
Padding (____ptrval____): 00 00 00 00 00 00 00 00 ........

After:

BUG test (Tainted: G B ): Right Redzone overwritten
...
Redzone (____ptrval____): bb bb bb bb bb bb bb bb ........
Object (____ptrval____): f6 f4 a5 40 1d e8 ...@..
Redzone (____ptrval____): 1a aa ..
Padding (____ptrval____): 00 00 00 00 00 00 00 00 ........

Fixes: d86bd1bece6f ("mm/slub: support left redzone")
Fixes: ffc79d288000 ("slub: use print_hex_dump")
Fixes: 2492268472e7 ("SLUB: change error reporting format to follow lockdep loosely")
Signed-off-by: Kees Cook <keescook@chromium.org>
---
Documentation/vm/slub.rst | 10 +++++-----
mm/slub.c | 14 +++++++-------
2 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/Documentation/vm/slub.rst b/Documentation/vm/slub.rst
index 289d231cee97..77c7a3331eda 100644
--- a/Documentation/vm/slub.rst
+++ b/Documentation/vm/slub.rst
@@ -181,7 +181,7 @@ SLUB Debug output
Here is a sample of slub debug output::

====================================================================
- BUG kmalloc-8: Redzone overwritten
+ BUG kmalloc-8: Right Redzone overwritten
--------------------------------------------------------------------

INFO: 0xc90f6d28-0xc90f6d2b. First byte 0x00 instead of 0xcc
@@ -189,10 +189,10 @@ Here is a sample of slub debug output::
INFO: Object 0xc90f6d20 @offset=3360 fp=0xc90f6d58
INFO: Allocated in get_modalias+0x61/0xf5 age=53 cpu=1 pid=554

- Bytes b4 0xc90f6d10: 00 00 00 00 00 00 00 00 5a 5a 5a 5a 5a 5a 5a 5a ........ZZZZZZZZ
- Object 0xc90f6d20: 31 30 31 39 2e 30 30 35 1019.005
- Redzone 0xc90f6d28: 00 cc cc cc .
- Padding 0xc90f6d50: 5a 5a 5a 5a 5a 5a 5a 5a ZZZZZZZZ
+ Bytes b4 (0xc90f6d10): 00 00 00 00 00 00 00 00 5a 5a 5a 5a 5a 5a 5a 5a ........ZZZZZZZZ
+ Object (0xc90f6d20): 31 30 31 39 2e 30 30 35 1019.005
+ Redzone (0xc90f6d28): 00 cc cc cc .
+ Padding (0xc90f6d50): 5a 5a 5a 5a 5a 5a 5a 5a ZZZZZZZZ

[<c010523d>] dump_trace+0x63/0x1eb
[<c01053df>] show_trace_log_lvl+0x1a/0x2f
diff --git a/mm/slub.c b/mm/slub.c
index 6d3574013b2f..f4f1d63f0ab9 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -698,15 +698,15 @@ static void print_trailer(struct kmem_cache *s, struct page *page, u8 *p)
p, p - addr, get_freepointer(s, p));

if (s->flags & SLAB_RED_ZONE)
- print_section(KERN_ERR, "Redzone ", p - s->red_left_pad,
+ print_section(KERN_ERR, "Redzone ", p - s->red_left_pad,
s->red_left_pad);
else if (p > addr + 16)
print_section(KERN_ERR, "Bytes b4 ", p - 16, 16);

- print_section(KERN_ERR, "Object ", p,
+ print_section(KERN_ERR, "Object ", p,
min_t(unsigned int, s->object_size, PAGE_SIZE));
if (s->flags & SLAB_RED_ZONE)
- print_section(KERN_ERR, "Redzone ", p + s->object_size,
+ print_section(KERN_ERR, "Redzone ", p + s->object_size,
s->inuse - s->object_size);

off = get_info_end(s);
@@ -718,7 +718,7 @@ static void print_trailer(struct kmem_cache *s, struct page *page, u8 *p)

if (off != size_from_object(s))
/* Beginning of the filler is the free pointer */
- print_section(KERN_ERR, "Padding ", p + off,
+ print_section(KERN_ERR, "Padding ", p + off,
size_from_object(s) - off);

dump_stack();
@@ -895,11 +895,11 @@ static int check_object(struct kmem_cache *s, struct page *page,
u8 *endobject = object + s->object_size;

if (s->flags & SLAB_RED_ZONE) {
- if (!check_bytes_and_report(s, page, object, "Redzone",
+ if (!check_bytes_and_report(s, page, object, "Left Redzone",
object - s->red_left_pad, val, s->red_left_pad))
return 0;

- if (!check_bytes_and_report(s, page, object, "Redzone",
+ if (!check_bytes_and_report(s, page, object, "Right Redzone",
endobject, val, s->inuse - s->object_size))
return 0;
} else {
@@ -914,7 +914,7 @@ static int check_object(struct kmem_cache *s, struct page *page,
if (val != SLUB_RED_ACTIVE && (s->flags & __OBJECT_POISON) &&
(!check_bytes_and_report(s, page, p, "Poison", p,
POISON_FREE, s->object_size - 1) ||
- !check_bytes_and_report(s, page, p, "Poison",
+ !check_bytes_and_report(s, page, p, "End Poison",
p + s->object_size - 1, POISON_END, 1)))
return 0;
/*
--
2.25.1