When running syzkaller with the newly reintroduced signed integer overflow sanitizer we encounter this report: UBSAN: signed-integer-overflow in ../fs/read_write.c:91:10 9223372036854775807 + 4096 cannot be represented in type 'loff_t' (aka 'long long') Call Trace: <TASK> dump_stack_lvl+0x93/0xd0 handle_overflow+0x171/0x1b0 generic_file_llseek_size+0x35b/0x380 ... amongst others: UBSAN: signed-integer-overflow in ../fs/read_write.c:1657:12 142606336 - -9223372036854775807 cannot be represented in type 'loff_t' (aka 'long long') ... UBSAN: signed-integer-overflow in ../fs/read_write.c:1666:11 9223372036854775807 - -9223231299366420479 cannot be represented in type 'loff_t' (aka 'long long') Fix the accidental overflow in these position and offset calculations by checking for negative position values, using check_add_overflow() helpers and clamping values to expected ranges. Link: https://github.com/llvm/llvm-project/pull/82432 [1] Closes: https://github.com/KSPP/linux/issues/358 Cc: linux-hardening@xxxxxxxxxxxxxxx Signed-off-by: Justin Stitt <justinstitt@xxxxxxxxxx> --- Changes in v3: - use check_add_overflow() instead of min() to keep old -EINVAL behavior (thanks Jan) - shorten UBSAN splat in commit log, reword commit log - Link to v2: https://lore.kernel.org/r/20240509-b4-sio-read_write-v2-1-018fc1e63392@xxxxxxxxxx Changes in v2: - fix some more cases syzkaller found in read_write.c - use min over min_t as the types are the same - Link to v1: https://lore.kernel.org/r/20240509-b4-sio-read_write-v1-1-06bec2022697@xxxxxxxxxx --- Historically, the signed integer overflow sanitizer did not work in the kernel due to its interaction with `-fwrapv` but this has since been changed [1] in the newest version of Clang. It was re-enabled in the kernel with Commit 557f8c582a9ba8ab ("ubsan: Reintroduce signed overflow sanitizer"). Here's the syzkaller reproducer: | # {Threaded:false Repeat:false RepeatTimes:0 Procs:1 Slowdown:1 Sandbox: | # SandboxArg:0 Leak:false NetInjection:false NetDevices:false | # NetReset:false Cgroups:false BinfmtMisc:false CloseFDs:false KCSAN:false | # DevlinkPCI:false NicVF:false USB:false VhciInjection:false Wifi:false | # IEEE802154:false Sysctl:false Swap:false UseTmpDir:false | # HandleSegv:false Repro:false Trace:false LegacyOptions:{Collide:false | # Fault:false FaultCall:0 FaultNth:0}} | r0 = openat$sysfs(0xffffffffffffff9c, &(0x7f0000000000)='/sys/kernel/address_bits', 0x0, 0x98) | lseek(r0, 0x7fffffffffffffff, 0x2) ... which was used against Kees' tree here (v6.8rc2): https://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git/log/?h=wip/v6.9-rc2/unsigned-overflow-sanitizer ... with this config: https://gist.github.com/JustinStitt/824976568b0f228ccbcbe49f3dee9bf4 --- fs/read_write.c | 20 +++++++++++++------- fs/remap_range.c | 12 ++++++------ 2 files changed, 19 insertions(+), 13 deletions(-) diff --git a/fs/read_write.c b/fs/read_write.c index d4c036e82b6c..8be30c8829a9 100644 --- a/fs/read_write.c +++ b/fs/read_write.c @@ -88,7 +88,8 @@ generic_file_llseek_size(struct file *file, loff_t offset, int whence, { switch (whence) { case SEEK_END: - offset += eof; + if (check_add_overflow(offset, eof, &offset)) + return -EINVAL; break; case SEEK_CUR: /* @@ -105,7 +106,9 @@ generic_file_llseek_size(struct file *file, loff_t offset, int whence, * like SEEK_SET. */ spin_lock(&file->f_lock); - offset = vfs_setpos(file, file->f_pos + offset, maxsize); + if (check_add_overflow(offset, file->f_pos, &offset)) + return -EINVAL; + offset = vfs_setpos(file, offset, maxsize); spin_unlock(&file->f_lock); return offset; case SEEK_DATA: @@ -1416,7 +1419,7 @@ static int generic_copy_file_checks(struct file *file_in, loff_t pos_in, struct inode *inode_in = file_inode(file_in); struct inode *inode_out = file_inode(file_out); uint64_t count = *req_count; - loff_t size_in; + loff_t size_in, in_sum, out_sum; int ret; ret = generic_file_rw_checks(file_in, file_out); @@ -1450,8 +1453,8 @@ static int generic_copy_file_checks(struct file *file_in, loff_t pos_in, if (IS_SWAPFILE(inode_in) || IS_SWAPFILE(inode_out)) return -ETXTBSY; - /* Ensure offsets don't wrap. */ - if (pos_in + count < pos_in || pos_out + count < pos_out) + if (check_add_overflow(pos_in, count, &in_sum) || + check_add_overflow(pos_out, count, &out_sum)) return -EOVERFLOW; /* Shorten the copy to EOF */ @@ -1467,8 +1470,8 @@ static int generic_copy_file_checks(struct file *file_in, loff_t pos_in, /* Don't allow overlapped copying within the same file. */ if (inode_in == inode_out && - pos_out + count > pos_in && - pos_out < pos_in + count) + out_sum > pos_in && + pos_out < in_sum) return -EINVAL; *req_count = count; @@ -1649,6 +1652,9 @@ int generic_write_check_limits(struct file *file, loff_t pos, loff_t *count) loff_t max_size = inode->i_sb->s_maxbytes; loff_t limit = rlimit(RLIMIT_FSIZE); + if (pos < 0) + return -EINVAL; + if (limit != RLIM_INFINITY) { if (pos >= limit) { send_sig(SIGXFSZ, current, 0); diff --git a/fs/remap_range.c b/fs/remap_range.c index de07f978ce3e..4570be4ef463 100644 --- a/fs/remap_range.c +++ b/fs/remap_range.c @@ -36,7 +36,7 @@ static int generic_remap_checks(struct file *file_in, loff_t pos_in, struct inode *inode_out = file_out->f_mapping->host; uint64_t count = *req_count; uint64_t bcount; - loff_t size_in, size_out; + loff_t size_in, size_out, in_sum, out_sum; loff_t bs = inode_out->i_sb->s_blocksize; int ret; @@ -44,17 +44,17 @@ static int generic_remap_checks(struct file *file_in, loff_t pos_in, if (!IS_ALIGNED(pos_in, bs) || !IS_ALIGNED(pos_out, bs)) return -EINVAL; - /* Ensure offsets don't wrap. */ - if (pos_in + count < pos_in || pos_out + count < pos_out) - return -EINVAL; + if (check_add_overflow(pos_in, count, &in_sum) || + check_add_overflow(pos_out, count, &out_sum)) + return -EOVERFLOW; size_in = i_size_read(inode_in); size_out = i_size_read(inode_out); /* Dedupe requires both ranges to be within EOF. */ if ((remap_flags & REMAP_FILE_DEDUP) && - (pos_in >= size_in || pos_in + count > size_in || - pos_out >= size_out || pos_out + count > size_out)) + (pos_in >= size_in || in_sum > size_in || + pos_out >= size_out || out_sum > size_out)) return -EINVAL; /* Ensure the infile range is within the infile. */ --- base-commit: 0106679839f7c69632b3b9833c3268c316c0a9fc change-id: 20240509-b4-sio-read_write-04a17d40620e Best regards, -- Justin Stitt <justinstitt@xxxxxxxxxx>
