From: Jiayuan Chen jiayuan.chen@linux.dev

Syzkaller reported a memory out-of-bounds bug [1]. This patch fixes two issues:

1. In vrealloc the KASAN_VMALLOC_VM_ALLOC flag is missing when unpoisoning the extended region. This flag is required to correctly associate the allocation with KASAN's vmalloc tracking.

Note: In contrast, vzalloc (via __vmalloc_node_range_noprof) explicitly sets KASAN_VMALLOC_VM_ALLOC and calls kasan_unpoison_vmalloc() with it. vrealloc must behave consistently — especially when reusing existing vmalloc regions — to ensure KASAN can track allocations correctly.

2. When vrealloc reuses an existing vmalloc region (without allocating new pages) KASAN generates a new tag, which breaks tag-based memory access tracking.

Introduce KASAN_VMALLOC_KEEP_TAG, a new KASAN flag that allows reusing the tag already attached to the pointer, ensuring consistent tag behavior during reallocation.

Pass KASAN_VMALLOC_KEEP_TAG and KASAN_VMALLOC_VM_ALLOC to the kasan_unpoison_vmalloc inside vrealloc_node_align_noprof().

[1]: https://syzkaller.appspot.com/bug?extid=997752115a851cb0cf36

Fixes: a0309faf1cb0 ("mm: vmalloc: support more granular vrealloc() sizing") Cc: stable@vger.kernel.org Reported-by: syzbot+997752115a851cb0cf36@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/68e243a2.050a0220.1696c6.007d.GAE@google.com/T/ Signed-off-by: Jiayuan Chen jiayuan.chen@linux.dev Co-developed-by: Maciej Wieczor-Retman maciej.wieczor-retman@intel.com Signed-off-by: Maciej Wieczor-Retman maciej.wieczor-retman@intel.com Reviewed-by: Andrey Konovalov andreyknvl@gmail.com --- include/linux/kasan.h | 1 + mm/kasan/hw_tags.c | 2 +- mm/kasan/shadow.c | 4 +++- mm/vmalloc.c | 4 +++- 4 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/include/linux/kasan.h b/include/linux/kasan.h index d12e1a5f5a9a..6d7972bb390c 100644 --- a/include/linux/kasan.h +++ b/include/linux/kasan.h @@ -28,6 +28,7 @@ typedef unsigned int __bitwise kasan_vmalloc_flags_t; #define KASAN_VMALLOC_INIT ((__force kasan_vmalloc_flags_t)0x01u) #define KASAN_VMALLOC_VM_ALLOC ((__force kasan_vmalloc_flags_t)0x02u) #define KASAN_VMALLOC_PROT_NORMAL ((__force kasan_vmalloc_flags_t)0x04u) +#define KASAN_VMALLOC_KEEP_TAG ((__force kasan_vmalloc_flags_t)0x08u)

#define KASAN_VMALLOC_PAGE_RANGE 0x1 /* Apply exsiting page range */ #define KASAN_VMALLOC_TLB_FLUSH 0x2 /* TLB flush */ diff --git a/mm/kasan/hw_tags.c b/mm/kasan/hw_tags.c index 1c373cc4b3fa..cbef5e450954 100644 --- a/mm/kasan/hw_tags.c +++ b/mm/kasan/hw_tags.c @@ -361,7 +361,7 @@ void *__kasan_unpoison_vmalloc(const void *start, unsigned long size, return (void *)start; }

- tag = kasan_random_tag(); + tag = (flags & KASAN_VMALLOC_KEEP_TAG) ? get_tag(start) : kasan_random_tag(); start = set_tag(start, tag);

/* Unpoison and initialize memory up to size. */ diff --git a/mm/kasan/shadow.c b/mm/kasan/shadow.c index 5d2a876035d6..5e47ae7fdd59 100644 --- a/mm/kasan/shadow.c +++ b/mm/kasan/shadow.c @@ -648,7 +648,9 @@ void *__kasan_unpoison_vmalloc(const void *start, unsigned long size, !(flags & KASAN_VMALLOC_PROT_NORMAL)) return (void *)start;

- start = set_tag(start, kasan_random_tag()); + if (unlikely(!(flags & KASAN_VMALLOC_KEEP_TAG))) + start = set_tag(start, kasan_random_tag()); + kasan_unpoison(start, size, false); return (void *)start; } diff --git a/mm/vmalloc.c b/mm/vmalloc.c index 798b2ed21e46..22a73a087135 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -4176,7 +4176,9 @@ void *vrealloc_node_align_noprof(const void *p, size_t size, unsigned long align */ if (size <= alloced_size) { kasan_unpoison_vmalloc(p + old_size, size - old_size, - KASAN_VMALLOC_PROT_NORMAL); + KASAN_VMALLOC_PROT_NORMAL | + KASAN_VMALLOC_VM_ALLOC | + KASAN_VMALLOC_KEEP_TAG); /* * No need to zero memory here, as unused memory will have * already been zeroed at initial allocation time or during