[GH-ISSUE #4387] Error mounting tmpfs: fs.c:499 fs_tmpfs: Invalid argument Error: proc 22812 cannot sync with peer: unexpected EOF

gitea-mirror commented

2026-05-05 09:18:37 -06:00

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Originally created by @darmon77 on GitHub (Jul 7, 2021).
Original GitHub issue: https://github.com/netblue30/firejail/issues/4387

Running having unexpected behavior in its default configuration in all its profiles.

firejail telegram-desktop
Reading profile /etc/firejail/telegram-desktop.profile
Reading profile /etc/firejail/telegram.profile
Reading profile /etc/firejail/disable-common.inc
Reading profile /etc/firejail/disable-devel.inc
Reading profile /etc/firejail/disable-exec.inc
Reading profile /etc/firejail/disable-interpreters.inc
Reading profile /etc/firejail/disable-passwdmgr.inc
Reading profile /etc/firejail/disable-programs.inc
Reading profile /etc/firejail/disable-shell.inc
Reading profile /etc/firejail/disable-xdg.inc
Reading profile /etc/firejail/whitelist-common.inc
Reading profile /etc/firejail/whitelist-runuser-common.inc
Reading profile /etc/firejail/whitelist-usr-share-common.inc
Reading profile /etc/firejail/whitelist-var-common.inc
Warning: private-cache feature is disabled in Firejail configuration file
Warning: private-etc feature is disabled in Firejail configuration file
Parent pid 22812, child pid 22815
Warning: cannot find /dev/null/utmp
Warning: An abstract unix socket for session D-BUS might still be available. Use --net or remove unix from --protocol set.
Error mounting tmpfs: fs.c:499 fs_tmpfs: Invalid argument
Error: proc 22812 cannot sync with peer: unexpected EOF
Peer 22815 unexpectedly exited with status 1

firejail --debug telegram-desktop
Mounting tmpfs on /usr/share, check owner: no
Error mounting tmpfs: fs.c:499 fs_tmpfs: Invalid argument
Error: proc 22956 cannot sync with peer: unexpected EOF
Peer 22959 unexpectedly exited with status 1

Environment

LSB Version: 1.0
Distributor ID: VoidLinux
Description: Void Linux
Release: rolling
Codename: void
firejail version 0.9.66

Compile time support:
- always force nonewprivs support is disabled
- AppArmor support is enabled
- AppImage support is enabled
- chroot support is enabled
- D-BUS proxy support is enabled
- file and directory whitelisting support is enabled
- file transfer support is enabled
- firetunnel support is enabled
- networking support is enabled
- output logging is enabled
- overlayfs support is disabled
- private-home support is enabled
- private-cache and tmpfs as user enabled
- SELinux support is disabled
- user namespace support is enabled
- X11 sandboxing support is enabled

Originally created by @darmon77 on GitHub (Jul 7, 2021). Original GitHub issue: https://github.com/netblue30/firejail/issues/4387 Running having unexpected behavior in its default configuration in all its profiles. firejail telegram-desktop Reading profile /etc/firejail/telegram-desktop.profile Reading profile /etc/firejail/telegram.profile Reading profile /etc/firejail/disable-common.inc Reading profile /etc/firejail/disable-devel.inc Reading profile /etc/firejail/disable-exec.inc Reading profile /etc/firejail/disable-interpreters.inc Reading profile /etc/firejail/disable-passwdmgr.inc Reading profile /etc/firejail/disable-programs.inc Reading profile /etc/firejail/disable-shell.inc Reading profile /etc/firejail/disable-xdg.inc Reading profile /etc/firejail/whitelist-common.inc Reading profile /etc/firejail/whitelist-runuser-common.inc Reading profile /etc/firejail/whitelist-usr-share-common.inc Reading profile /etc/firejail/whitelist-var-common.inc Warning: private-cache feature is disabled in Firejail configuration file Warning: private-etc feature is disabled in Firejail configuration file Parent pid 22812, child pid 22815 Warning: cannot find /dev/null/utmp Warning: An abstract unix socket for session D-BUS might still be available. Use --net or remove unix from --protocol set. **Error mounting tmpfs: fs.c:499 fs_tmpfs: Invalid argument Error: proc 22812 cannot sync with peer: unexpected EOF Peer 22815 unexpectedly exited with status 1** firejail --debug telegram-desktop **Mounting tmpfs on /usr/share, check owner: no Error mounting tmpfs: fs.c:499 fs_tmpfs: Invalid argument Error: proc 22956 cannot sync with peer: unexpected EOF Peer 22959 unexpectedly exited with status 1** **Environment** - LSB Version: 1.0 Distributor ID: VoidLinux Description: Void Linux Release: rolling Codename: void - firejail version 0.9.66 Compile time support: - always force nonewprivs support is disabled - AppArmor support is enabled - AppImage support is enabled - chroot support is enabled - D-BUS proxy support is enabled - file and directory whitelisting support is enabled - file transfer support is enabled - firetunnel support is enabled - networking support is enabled - output logging is enabled - overlayfs support is disabled - private-home support is enabled - private-cache and tmpfs as user enabled - SELinux support is disabled - user namespace support is enabled - X11 sandboxing support is enabled

gitea-mirror

2026-05-05 09:18:37 -06:00

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gitea-mirror commented

2026-05-05 09:18:41 -06:00

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@smitsohu commented on GitHub (Jul 12, 2021):

Hi @darmon77, thanks for reporting this.

Can you please post the output of

ls -ld /usr /usr/share
findmnt --target /usr/share

@smitsohu commented on GitHub (Jul 12, 2021): Hi @darmon77, thanks for reporting this. Can you please post the output of ``` ls -ld /usr /usr/share findmnt --target /usr/share ```

gitea-mirror commented

2026-05-05 09:18:42 -06:00

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@darmon77 commented on GitHub (Jul 12, 2021):

root@dennis:|⇒ ls -ld /usr /usr/share
drwxr-xr-x 10 root root 4096 Feb 10 01:25 /usr
drwxr-xr-x 220 root root 4096 Jul 2 23:09 /usr/share
root@dennis|⇒ findmnt --target /usr/share
TARGET SOURCE FSTYPE OPTIONS
/ /dev/mapper/data77--vg-root ext4 rw,relatime

@darmon77 commented on GitHub (Jul 12, 2021): root@dennis:|⇒ ls -ld /usr /usr/share drwxr-xr-x 10 root root 4096 Feb 10 01:25 /usr drwxr-xr-x 220 root root 4096 Jul 2 23:09 /usr/share root@dennis|⇒ findmnt --target /usr/share TARGET SOURCE FSTYPE OPTIONS / /dev/mapper/data77--vg-root ext4 rw,relatime

gitea-mirror commented

2026-05-05 09:18:43 -06:00

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@D-RX commented on GitHub (Jul 13, 2021):

Same problem on Void Linux, using musl, but with just:
firejail firefox
Error output is essentially the same.

I've run strace and gdb on firejail with the args set to firefox. The problem is in the call to mount in fs.c:498 (function fs_tmpfs). Arguments to mount are:
source (rdi) => "tmpfs"
target (rsi) => "/proc/self/fd/8", which is a symbolic link to /usr/share
filesystem (rdx) => "tmpfs"
mountflags (r10) = 0x1
data (r8) => "mode=755,uid=0,gid=0"
The call to mount returns EINVAL or -1.
The stack trace shows that this is called from tmpfs_topdirs, which was called from fs_whitelist in a child process __cloned from firejail.

strace shows that there are several successful calls to mount with filesystem set to "tmpfs" before this.

I have essentially the same output as darmon77 to (just a different device name from fndmnt):

ls -ld /usr /usr/share
findmnt --target /usr/share

@D-RX commented on GitHub (Jul 13, 2021): Same problem on Void Linux, using musl, but with just: `firejail firefox` Error output is essentially the same. I've run `strace` and `gdb` on firejail with the args set to firefox. The problem is in the call to `mount` in fs.c:498 (function `fs_tmpfs`). Arguments to mount are: _source_ (rdi) => "tmpfs" _target_ (rsi) => "/proc/self/fd/8", which is a symbolic link to /usr/share _filesystem_ (rdx) => "tmpfs" _mountflags_ (r10) = 0x1 _data_ (r8) => "mode=755,uid=0,gid=0" The call to mount returns `EINVAL` or -1. The stack trace shows that this is called from `tmpfs_topdirs`, which was called from `fs_whitelist` in a child process `__clone`d from firejail. `strace` shows that there are several successful calls to `mount` with filesystem set to "tmpfs" before this. I have essentially the same output as **darmon77** to (just a different device name from `fndmnt`): ``` ls -ld /usr /usr/share findmnt --target /usr/share ```

gitea-mirror commented

2026-05-05 09:18:44 -06:00

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@smitsohu commented on GitHub (Jul 13, 2021):

At first I thought we are carrying over a mountflag that is not compatible with tmpfs, but this doesn't seem to be the case.

mountflags (r10) = 0x1

Instead we have wrong mountflags, which is a separate and possibly related bug: 0x1 is the read-only flag, which Firejail actually is supposed to remove:

110a74f094/src/firejail/fs.c (L488-L492)

@smitsohu commented on GitHub (Jul 13, 2021): At first I thought we are carrying over a mountflag that is not compatible with `tmpfs`, but this doesn't seem to be the case. > `mountflags (r10) = 0x1` Instead we have wrong mountflags, which is a separate and possibly related bug: `0x1` is the read-only flag, which Firejail actually is supposed to remove: https://github.com/netblue30/firejail/blob/110a74f094abcb4f2763d76e204fb3c9743fa9a1/src/firejail/fs.c#L488-L492

gitea-mirror commented

2026-05-05 09:18:45 -06:00

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@smitsohu commented on GitHub (Jul 13, 2021):

Just for the record, I cannot reproduce on Debian or Fedora at the moment.

@smitsohu commented on GitHub (Jul 13, 2021): Just for the record, I cannot reproduce on Debian or Fedora at the moment.

gitea-mirror commented

2026-05-05 09:18:45 -06:00

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@D-RX commented on GitHub (Jul 13, 2021):

Sorry, there was a mistake in my earlier post. The value in mountflags for the mount syscall should actually be 0x26. I was looking at the call to mount just at line fs.c:498, but stepped by line rather than instruction. Following to the syscall by instruction shows that mountflags (r10) is set to 0x26 (from rcx) just before the syscall instruction (the rcx vs. r10 is just user-space vs. kernel-space calling conventions). The return value from the syscall to mount is -22 (decimal).

Also, I understand that this bug does not appear in Void Linux when using glibc, but only when using musl.

@D-RX commented on GitHub (Jul 13, 2021): Sorry, there was a mistake in my earlier post. The value in _mountflags_ for the `mount` syscall should actually be `0x26`. I was looking at the call to `mount` just at line fs.c:498, but stepped by line rather than instruction. Following to the `syscall` by instruction shows that _mountflags_ (r10) is set to `0x26` (from rcx) just before the `syscall` instruction (the rcx vs. r10 is just user-space vs. kernel-space calling conventions). The return value from the `syscall` to `mount` is `-22` (decimal). Also, I understand that this bug does not appear in Void Linux when using glibc, but only when using musl.

gitea-mirror commented

2026-05-05 09:18:46 -06:00

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@smitsohu commented on GitHub (Jul 13, 2021):

The value in mountflags for the mount syscall should actually be 0x26

Thanks. We need to remove MS_REMOUNT. I'll put a fix shortly.

@smitsohu commented on GitHub (Jul 13, 2021): > The value in mountflags for the mount syscall should actually be 0x26 Thanks. We need to remove `MS_REMOUNT`. I'll put a fix shortly.

gitea-mirror commented

2026-05-05 09:18:47 -06:00

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@D-RX commented on GitHub (Jul 20, 2021):

I can verify that modifying the value ANDed with the mount flags in the firejail binary to effect the same as your commit ba5f5c8 i.e. to include clearing MS_REMOUNT:
unsigned long flags = buf.f_flag & ~(MS_RDONLY|MS_BIND|MS_REMOUNT);
(that is, the ANDed value goes from ... FF EF FE -> ... FF EF DE)
does fix the bug in Void Linux using musl.
Thanks!

@D-RX commented on GitHub (Jul 20, 2021): I can verify that modifying the value `AND`ed with the mount flags in the firejail binary to effect the same as your commit `ba5f5c8` i.e. to include clearing `MS_REMOUNT`: `unsigned long flags = buf.f_flag & ~(MS_RDONLY|MS_BIND|MS_REMOUNT);` (that is, the `AND`ed value goes from `... FF EF FE` -> `... FF EF DE`) does fix the bug in Void Linux using musl. Thanks!

gitea-mirror commented

2026-05-05 09:18:48 -06:00

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@smitsohu commented on GitHub (Jul 22, 2021):

Guess we can close if there is nothing left to do. Thanks everyone!

@smitsohu commented on GitHub (Jul 22, 2021): Guess we can close if there is nothing left to do. Thanks everyone!

gitea-mirror referenced this issue

2026-05-05 10:20:41 -06:00

[PR #2649] [MERGED] Add a conditional to control DRM/noexec exception for browsers #4467

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[GH-ISSUE #4387] Error mounting tmpfs: fs.c:499 fs_tmpfs: Invalid argument Error: proc 22812 cannot sync with peer: unexpected EOF #2649