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In 64bit system. sb->s_maxbytes of shmem filesystem is MAX_LFS_FILESIZE, which equal LLONG_MAX. If offset > LLONG_MAX - PAGE_SIZE, offset + len < LLONG_MAX in shmem_fallocate, which will pass the checking in vfs_fallocate. /* Check for wrap through zero too */ if (((offset + len) > inode->i_sb->s_maxbytes) || ((offset + len) < 0)) return -EFBIG; loff_t unmap_start = round_up(offset, PAGE_SIZE) in shmem_fallocate causes a overflow. Syzkaller reports a overflow problem in mm/shmem: UBSAN: Undefined behaviour in mm/shmem.c:2014:10 signed integer overflow: '9223372036854775807 + 1' cannot be represented in type 'long long int' CPU: 0 PID:17076 Comm: syz-executor0 Not tainted 4.1.46+ #1 Hardware name: linux, dummy-virt (DT) Call trace: dump_backtrace+0x0/0x2c8 arch/arm64/kernel/traps.c:100 show_stack+0x20/0x30 arch/arm64/kernel/traps.c:238 __dump_stack lib/dump_stack.c:15 [inline] ubsan_epilogue+0x18/0x70 lib/ubsan.c:164 handle_overflow+0x158/0x1b0 lib/ubsan.c:195 shmem_fallocate+0x6d0/0x820 mm/shmem.c:2104 vfs_fallocate+0x238/0x428 fs/open.c:312 SYSC_fallocate fs/open.c:335 [inline] SyS_fallocate+0x54/0xc8 fs/open.c:239 The highest bit of unmap_start will be appended with sign bit 1 (overflow) when calculate shmem_falloc.start: shmem_falloc.start = unmap_start >> PAGE_SHIFT. Fix it by casting the type of unmap_start to u64, when right shifted. This bug is found in LTS Linux 4.1. It also seems to exist in mainline. Link: http://lkml.kernel.org/r/1573867464-5107-1-git-send-email-chenjun102@huawei.com Signed-off-by: Chen Jun <chenjun102@huawei.com> Reviewed-by: Andrew Morton <akpm@linux-foundation.org> Cc: Hugh Dickins <hughd@google.com> Cc: Qian Cai <cai@lca.pw> Cc: Kefeng Wang <wangkefeng.wang@huawei.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> |
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| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
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| MAINTAINERS | ||
| Makefile | ||
| README | ||
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.