Subject: bug#59382: cp(1) tries to allocate too much memory if filesystem blocksizes are unusual

From: Korn Andras <[email-masked]>
Date: Sat, 19 Nov 2022 09:14:50 +0100

Hi,

on zfs, newfstatat() can return an st_blksize that is approximately equal to the file size in bytes (if the file fit into a single zfs record).

The block size for filesystems can also be quite large (currently, up to 16M).

The code at https://github.com/coreutils/coreutils/blob/master/src/copy.c#L1343 will try to compute the least common multiple of the input and output block sizes, then allocate a buffer of that size using mmap(). With such unusual block sizes, the least common multiple can be very large, causing the mmap() to return ENOMEM and cp to abort with "memory exhausted".

Example:

openat(AT_FDCWD, "tmp", O_RDONLY|O_PATH|O_DIRECTORY) = 3</t/tmp>
newfstatat(AT_FDCWD, "usr/src/zfs-2.1.6/configure", {st_dev=makedev(0, 0x30), st_ino=29267, st_mode=S_IFREG|0755, st_nlink=1, st_uid=0, st_gid=0, st_blksize=2647552, st_blocks=5177, st_size=2647046, st_atime=1668786119 /* 2022-11-18T16:41:59.760703544+0100 */, st_atime_nsec=760703544, st_mtime=1667705386 /* 2022-11-06T04:29:46+0100 */, st_mtime_nsec=0, st_ctime=1668785062 /* 2022-11-18T16:24:22.866737598+0100 */, st_ctime_nsec=866737598}, AT_SYMLINK_NOFOLLOW) = 0
newfstatat(3</t/tmp>, "configure", {st_dev=makedev(0, 0x32), st_ino=3838, st_mode=S_IFREG|0700, st_nlink=1, st_uid=0, st_gid=0, st_blksize=4194304, st_blocks=1, st_size=0, st_atime=1668788205 /* 2022-11-18T17:16:45.416328293+0100 */, st_atime_nsec=416328293, st_mtime=1668788255 /* 2022-11-18T17:17:35.809758585+0100 */, st_mtime_nsec=809758585, st_ctime=1668788255 /* 2022-11-18T17:17:35.809758585+0100 */, st_ctime_nsec=809758585}, 0) = 0
openat(AT_FDCWD, "usr/src/zfs-2.1.6/configure", O_RDONLY|O_NOFOLLOW) = 4</t/usr/src/zfs-2.1.6/configure>
newfstatat(4</t/usr/src/zfs-2.1.6/configure>, "", {st_dev=makedev(0, 0x30), st_ino=29267, st_mode=S_IFREG|0755, st_nlink=1, st_uid=0, st_gid=0, st_blksize=2647552, st_blocks=5177, st_size=2647046, st_atime=1668786119 /* 2022-11-18T16:41:59.760703544+0100 */, st_atime_nsec=760703544, st_mtime=1667705386 /* 2022-11-06T04:29:46+0100 */, st_mtime_nsec=0, st_ctime=1668785062 /* 2022-11-18T16:24:22.866737598+0100 */, st_ctime_nsec=866737598}, AT_EMPTY_PATH) = 0
openat(3</t/tmp>, "configure", O_WRONLY|O_TRUNC) = 5</t/tmp/configure>
ioctl(5</t/tmp/configure>, BTRFS_IOC_CLONE or FICLONE, 4) = -1 EXDEV (Invalid cross-device link)
newfstatat(5</t/tmp/configure>, "", {st_dev=makedev(0, 0x32), st_ino=3838, st_mode=S_IFREG|0700, st_nlink=1, st_uid=0, st_gid=0, st_blksize=4194304, st_blocks=1, st_size=0, st_atime=1668788205 /* 2022-11-18T17:16:45.416328293+0100 */, st_atime_nsec=416328293, st_mtime=1668788266 /* 2022-11-18T17:17:46.326056957+0100 */, st_mtime_nsec=326056957, st_ctime=1668788266 /* 2022-11-18T17:17:46.326056957+0100 */, st_ctime_nsec=326056957}, AT_EMPTY_PATH) = 0
fadvise64(4</t/usr/src/zfs-2.1.6/configure>, 0, 0, POSIX_FADV_SEQUENTIAL) = 0
copy_file_range(4</t/usr/src/zfs-2.1.6/configure>, NULL, 5</t/tmp/configure>, NULL, 9223372035781033984, 0) = -1 EXDEV (Invalid cross-device link)
mmap(NULL, 21688754176, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = -1 ENOMEM (Cannot allocate memory)
brk(0x55a7fa4b0000)                     = 0x55a2ed8ab000
mmap(NULL, 21689794560, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = -1 ENOMEM (Cannot allocate memory)
openat(AT_FDCWD, "/usr/share/locale/en_US.UTF-8/LC_MESSAGES/coreutils.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/share/locale/en_US.utf8/LC_MESSAGES/coreutils.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/share/locale/en_US/LC_MESSAGES/coreutils.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/share/locale/en.UTF-8/LC_MESSAGES/coreutils.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/share/locale/en.utf8/LC_MESSAGES/coreutils.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/share/locale/en/LC_MESSAGES/coreutils.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
write(2</dev/pts/3<char 136:3>>, "cp: ", 4) = 4
write(2</dev/pts/3<char 136:3>>, "memory exhausted", 16) = 16
write(2</dev/pts/3<char 136:3>>, "\n", 1) = 1
lseek(0</dev/pts/3<char 136:3>>, 0, SEEK_CUR) = -1 ESPIPE (Illegal seek)
close(0</dev/pts/3<char 136:3>>)        = 0
close(1</dev/pts/3<char 136:3>>)        = 0
close(2</dev/pts/3<char 136:3>>)        = 0
exit_group(1)                           = ?

I think cp(1) shouldn't insist on using the lcm if it's very large; additionally, it should never try to allocate a buffer that is (much) larger than the source file.

Perhaps you could also try to use successively smaller buffers if allocating a large one fails?

András

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