`fs::copy` fails copying '.git' dir from Linux to Windows(SMB)

[TobisLee]

I tried to copy a git repository from Linux host to Windows host using yazi. And I noticed that there are some files in .git dir are copied failed. The error is permission denied. I reported to yazi (see sxyazi/yazi#1703). But it seems yazi just call the std::fs::copy to copy files. And I tried the following code:

use std::fs;

fn main() {
    fs::copy(
        "/home/xxx/.git/objects/pack/pack-d2e6xxxc2.idx",
        "/win-share/pack-d2e6xxxc2.idx").unwrap();
}

I expected to see this happen:
File pack-d2e6xxxc2.idx is copied to Windows directory.

Instead, this happened:

Error: Os { code: 13, kind: PermissionDenied, message: "Permission denied" }

Meta

rustc --version --verbose:

rustc 1.79.0 (129f3b996 2024-06-10)
binary: rustc
commit-hash: 129f3b9964af4d4a709d1383930ade12dfe7c081
commit-date: 2024-06-10
host: x86_64-unknown-linux-gnu
release: 1.79.0
LLVM version: 18.1.7

Backtrace

stack backtrace:
   0: rust_begin_unwind
             at /rustc/129f3b9964af4d4a709d1383930ade12dfe7c081/library/std/src/panicking.rs:652:5
   1: core::panicking::panic_fmt
             at /rustc/129f3b9964af4d4a709d1383930ade12dfe7c081/library/core/src/panicking.rs:72:14
   2: core::result::unwrap_failed
             at /rustc/129f3b9964af4d4a709d1383930ade12dfe7c081/library/core/src/result.rs:1654:5
   3: core::result::Result<T,E>::unwrap
             at /rustc/129f3b9964af4d4a709d1383930ade12dfe7c081/library/core/src/result.rs:1077:23
   4: fs_copy::main
             at ./src/main.rs:4:5
   5: core::ops::function::FnOnce::call_once
             at /rustc/129f3b9964af4d4a709d1383930ade12dfe7c081/library/core/src/ops/function.rs:250:5

[bjorn3]

Do you actually have permission? Does copying using cp on the commandline work? If both are true can you show an strace of the failing rust program?

[TobisLee]

Do you actually have permission?

Yeah, I have the read permission for the file, and the write permission for the target folder.

Does copying using cp on the commandline work?

Yeah, cp does copy the file with no error.

I run the strace ./target/debug/fs-copy

execve("./target/debug/fs-copy", ["./target/debug/fs-copy"], 0x7fff3c076090 /* 66 vars */) = 0
brk(NULL)                               = 0x56c871f58000
access("/etc/ld.so.preload", R_OK)      = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=176339, ...}) = 0
mmap(NULL, 176339, PROT_READ, MAP_PRIVATE, 3, 0) = 0x76f1cd547000
close(3)                                = 0
openat(AT_FDCWD, "/usr/lib/libgcc_s.so.1", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\0\0\0\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0644, st_size=915712, ...}) = 0
mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x76f1cd545000
mmap(NULL, 184808, PROT_READ, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x76f1cd517000
mmap(0x76f1cd51b000, 147456, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x4000) = 0x76f1cd51b000
mmap(0x76f1cd53f000, 16384, PROT_READ, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x28000) = 0x76f1cd53f000
mmap(0x76f1cd543000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x2b000) = 0x76f1cd543000
close(3)                                = 0
openat(AT_FDCWD, "/usr/lib/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\340_\2\0\0\0\0\0"..., 832) = 832
pread64(3, "\6\0\0\0\4\0\0\0@\0\0\0\0\0\0\0@\0\0\0\0\0\0\0@\0\0\0\0\0\0\0"..., 784, 64) = 784
fstat(3, {st_mode=S_IFREG|0755, st_size=2014520, ...}) = 0
pread64(3, "\6\0\0\0\4\0\0\0@\0\0\0\0\0\0\0@\0\0\0\0\0\0\0@\0\0\0\0\0\0\0"..., 784, 64) = 784
mmap(NULL, 2034616, PROT_READ, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x76f1cd326000
mmap(0x76f1cd34a000, 1511424, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x24000) = 0x76f1cd34a000
mmap(0x76f1cd4bb000, 319488, PROT_READ, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x195000) = 0x76f1cd4bb000
mmap(0x76f1cd509000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1e3000) = 0x76f1cd509000
mmap(0x76f1cd50f000, 31672, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x76f1cd50f000
close(3)                                = 0
mmap(NULL, 12288, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x76f1cd323000
arch_prctl(ARCH_SET_FS, 0x76f1cd323780) = 0
set_tid_address(0x76f1cd323a50)         = 8421
set_robust_list(0x76f1cd323a60, 24)     = 0
rseq(0x76f1cd3240a0, 0x20, 0, 0x53053053) = 0
mprotect(0x76f1cd509000, 16384, PROT_READ) = 0
mprotect(0x76f1cd543000, 4096, PROT_READ) = 0
mprotect(0x56c86b4d1000, 12288, PROT_READ) = 0
mprotect(0x76f1cd5ad000, 8192, PROT_READ) = 0
prlimit64(0, RLIMIT_STACK, NULL, {rlim_cur=8192*1024, rlim_max=RLIM64_INFINITY}) = 0
munmap(0x76f1cd547000, 176339)          = 0
poll([{fd=0, events=0}, {fd=1, events=0}, {fd=2, events=0}], 3, 0) = 0 (Timeout)
rt_sigaction(SIGPIPE, {sa_handler=SIG_IGN, sa_mask=[PIPE], sa_flags=SA_RESTORER|SA_RESTART, sa_restorer=0x76f1cd3631d0}, {sa_handler=SIG_DFL, sa_mask=[], sa_flags=0}, 8) = 0
getrandom("\xd6\x5d\xa8\x65\xa2\x1e\x5e\x63", 8, GRND_NONBLOCK) = 8
brk(NULL)                               = 0x56c871f58000
brk(0x56c871f79000)                     = 0x56c871f79000
openat(AT_FDCWD, "/proc/self/maps", O_RDONLY|O_CLOEXEC) = 3
prlimit64(0, RLIMIT_STACK, NULL, {rlim_cur=8192*1024, rlim_max=RLIM64_INFINITY}) = 0
fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0
read(3, "56c86b47f000-56c86b485000 r--p 0"..., 1024) = 1024
read(3, "p 001e3000 103:02 658867        "..., 1024) = 1024
read(3, "xp 00001000 103:02 658789       "..., 1024) = 549
close(3)                                = 0
sched_getaffinity(8421, 32, [0 1 2 3 4 5 6 7 8 9 10 11]) = 8
rt_sigaction(SIGSEGV, NULL, {sa_handler=SIG_DFL, sa_mask=[], sa_flags=0}, 8) = 0
rt_sigaction(SIGSEGV, {sa_handler=0x56c86b4a4e40, sa_mask=[], sa_flags=SA_RESTORER|SA_ONSTACK|SA_SIGINFO, sa_restorer=0x76f1cd3631d0}, NULL, 8) = 0
rt_sigaction(SIGBUS, NULL, {sa_handler=SIG_DFL, sa_mask=[], sa_flags=0}, 8) = 0
rt_sigaction(SIGBUS, {sa_handler=0x56c86b4a4e40, sa_mask=[], sa_flags=SA_RESTORER|SA_ONSTACK|SA_SIGINFO, sa_restorer=0x76f1cd3631d0}, NULL, 8) = 0
sigaltstack(NULL, {ss_sp=NULL, ss_flags=SS_DISABLE, ss_size=0}) = 0
mmap(NULL, 12288, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS|MAP_STACK, -1, 0) = 0x76f1cd570000
mprotect(0x76f1cd570000, 4096, PROT_NONE) = 0
sigaltstack({ss_sp=0x76f1cd571000, ss_flags=0, ss_size=8192}, NULL) = 0
openat(AT_FDCWD, "/home/tlss/repos/my-own-swordsmam-bilibili-danmu/.git/objects/pack/pack-d2e66015bbbc4e376941d6b59325b32cd94baac2.idx", O_RDONLY|O_CLOEXEC) = 3
statx(3, "", AT_STATX_SYNC_AS_STAT|AT_EMPTY_PATH, STATX_ALL, {stx_mask=STATX_ALL|STATX_MNT_ID, stx_attributes=0, stx_mode=S_IFREG|0444, stx_size=21176, ...}) = 0
openat(AT_FDCWD, "/home/tlss/win-share/18tb/temp/target.idx", O_WRONLY|O_CREAT|O_TRUNC|O_CLOEXEC, 0100444) = -1 EACCES (Permission denied)
close(3)                                = 0
write(2, "thread '", 8thread ')                 = 8
write(2, "main", 4main)                     = 4
write(2, "' panicked at ", 14' panicked at )          = 14
write(2, "src/main.rs", 11src/main.rs)             = 11
write(2, ":", 1:)                        = 1
write(2, "6", 16)                        = 1
write(2, ":", 1:)                        = 1
write(2, "54", 254)                       = 2
write(2, ":\n", 2:
)                      = 2
write(2, "called `Result::unwrap()` on an "..., 114called `Result::unwrap()` on an `Err` value: Os { code: 13, kind: PermissionDenied, message: "Permission denied" }) = 114
write(2, "\n", 1
)                       = 1
write(2, "note: run with `RUST_BACKTRACE=1"..., 78note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
) = 78
futex(0x76f1cd544070, FUTEX_WAKE_PRIVATE, 2147483647) = 0
sigaltstack({ss_sp=NULL, ss_flags=SS_DISABLE, ss_size=8192}, NULL) = 0
munmap(0x76f1cd570000, 12288)           = 0
exit_group(101)                         = ?
+++ exited with 101 +++

[the8472]

What's the windows share mounted with? The kernel's SMB driver or a FUSE implementation? You can check via
grep win-share /proc/mounts

[the8472]

openat(AT_FDCWD, "/home/tlss/win-share/18tb/temp/target.idx", O_WRONLY|O_CREAT|O_TRUNC|O_CLOEXEC, 0100444)

Hrrm, the 1 there looks sus, maybe we shouldn't be passing through all the bits from st_mode.

On the other hand the openat2 manpage says:

          Whereas openat(2) ignores bits other than those in the range 07777 in its mode argument, openat2() returns an error if how.mode con‐
          tains  bits other than 07777.  Similarly, an error is returned if openat2() is called with a nonzero how.mode and how.flags does not
          contain O_CREAT or O_TMPFILE.

so the extra bits should be fine with openat.

[the8472]

Or maybe windows/smb doesn't support unix semantics of open where the current FD permissions can be different from the on-disk mode that only affect subsequent opens.

@TobisLee does the copy succeed if you make the source file writable?

[TobisLee]

Hey @the8472, thanks for your help. Here's some information that might be useful.

What's the windows share mounted with?

I use the kernel's SMB driver.

> grep win-share /proc/mounts
//192.168.2.5/h /home/tlss/win-share/18tb cifs rw,relatime,vers=3.1.1,cache=strict,username=tlss1,uid=1000,forceuid,gid=0,noforcegid,addr=192.168.2.5,file_mode=0755,dir_mode=0755,soft,nounix,serverino,mapposix,reparse=nfs,rsize=4194304,wsize=4194304,bsize=1048576,retrans=1,echo_interval=60,actimeo=1,closetimeo=1 0 0

does the copy succeed if you make the source file writable?

No, still got the same error.

[the8472]

Then does the target file already exist with permissions that would prevent it from being overwritten?

[TobisLee]

Ah, yes, there is a target file already exists, after I delete the file, and rerun the code, the target file is copied successfully.

[the8472]

Then I think there's no problem here. cp also has the same behavior where it does not clobber write-protected destination files

$ touch a && touch b && chmod -w b && cp a b
cp: cannot create regular file 'b': Permission denied

[TobisLee]

Sorry, I am not sure I understand you correctly.

As you said, when the target file ('b') exists, the copy will fail. But at the first time, there is no target file in the destination directory, and I run the code, I got the error. It's more like:

$ touch a && chmod -w a && cp a b

And the second time, after I add writable permission to source file, the code run successfully.

[the8472]

I'm not sure if I understand the order of events correctly.
You previously said it copied successfully after deleting the file.
Now you outline a few steps but also say "the second time", so there are more steps?

Can you provide complete procedures of what does and what doesn't work?

[TobisLee]

If the file have write permission, then the code will run successfully, the file will be copied. Otherwise, the code will fail. The cp command copy the file successfully whether it has write permission or not.

I record a video to show the complete procedures.

_20241001_171130.webm

[the8472]

Ok, then I suspect this is an issue with windows or the cifs driver that it can't open-create a file for writing and simultanously give it read-only permissions.

Setting the permissions early is intentional: #58803

Can you verify that this fails on the windows share but succeeds on your local drives?

use std::os::unix::fs::OpenOptionsExt;
use std::fs::OpenOptions;
fn main() {
    let path = "....";
    OpenOptions::new().mode(0o444).write(true).create(true).truncate(true).open(path).expect("should succeed");
}