Commit 78ff64081949 ("vfs: Convert tracefs to use the new mount API") converted tracefs to use the new mount APIs caused mount options (e.g. gid=<gid>) to not take effect.

The tracefs superblock can be updated from multiple paths: - on fs_initcall() to init_trace_printk_function_export() - form a work queue to initialize eventfs tracer_init_tracefs_work_func() - fsconfig() syscall to mount or remount of tracefs

The tracefs super block root inode gets created early on in init_trace_printk_function_export().

With the new mount API tracefs effectively uses get_tree_single() instead of the old API mount_single().

Previously, mount_single() ensured that the options are always applied to the superblock root inode: (1) If the root inode didn't exist, called fill_super() to create it and apply the options. (2) If the root inode exists, called reconfigure_single() which effectively called tracefs_apply_options() to parse and apply options to the subperblock's fs_info and inode and remount eventfs (if necessary)

On the other hand, get_tree_single() effectively calls vfs_get_super() which: (3) If the root inode doesn't exists calls fill_super() to create it and apply the options. (4) If the root inode already exists, updates the fs_context root with the superblock's root inode.

(4) above is always the case for tracefs mounts, since the super block's root inode will already be created by init_trace_printk_function_export().

This means that the mount option get ignored: - Since it isn't applied to the super block's root inode, it doesn't get inherited by the children. - Since eventfs is initialized from a separate work queue and before call to mount with the options, and it doesn't get remounted for mount.

Ensure that the mount options are applied to the super block and eventfs is remounted to respect the mount options.

[1] https://lore.kernel.org/r/536e99d3-345c-448b-adee-a21389d7ab4b@redhat.com/

Fixes: 78ff64081949 ("vfs: Convert tracefs to use the new mount API") Cc: Eric Sandeen sandeen@redhat.com Cc: David Howells dhowells@redhat.com Cc: Steven Rostedt rostedt@goodmis.org Cc: Masami Hiramatsu mhiramat@kernel.org Signed-off-by: Kalesh Singh kaleshsingh@google.com ---

Changes in v2: - Update the commit title to reflect that all mount options are affected not only gid, per Eric

fs/tracefs/inode.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/fs/tracefs/inode.c b/fs/tracefs/inode.c index 1748dff58c3b..cfc614c638da 100644 --- a/fs/tracefs/inode.c +++ b/fs/tracefs/inode.c @@ -392,6 +392,9 @@ static int tracefs_reconfigure(struct fs_context *fc) struct tracefs_fs_info *sb_opts = sb->s_fs_info; struct tracefs_fs_info *new_opts = fc->s_fs_info;

+ if (!new_opts) + return 0; + sync_filesystem(sb); /* structure copy of new mount options to sb */ *sb_opts = *new_opts; @@ -478,14 +481,17 @@ static int tracefs_fill_super(struct super_block *sb, struct fs_context *fc) sb->s_op = &tracefs_super_operations; sb->s_d_op = &tracefs_dentry_operations;

- tracefs_apply_options(sb, false); - return 0; }

static int tracefs_get_tree(struct fs_context *fc) { - return get_tree_single(fc, tracefs_fill_super); + int err = get_tree_single(fc, tracefs_fill_super); + + if (err) + return err; + + return tracefs_reconfigure(fc); }

static void tracefs_free_fc(struct fs_context *fc)

Add a selftest to check that the tracefs gid mount option is applied correctly.

./ftracetest test.d/00basic/mount_options.tc

Use the new readme string "[gid=<gid>] as a requirement and also update test_ownership.tc requirements to use this.

Cc: Eric Sandeen sandeen@redhat.com Cc: David Howells dhowells@redhat.com Cc: Steven Rostedt rostedt@goodmis.org Cc: Masami Hiramatsu mhiramat@kernel.org Signed-off-by: Kalesh Singh kaleshsingh@google.com --- .../ftrace/test.d/00basic/mount_options.tc | 101 ++++++++++++++++++ .../ftrace/test.d/00basic/test_ownership.tc | 16 +-- .../testing/selftests/ftrace/test.d/functions | 25 +++++ 3 files changed, 129 insertions(+), 13 deletions(-) create mode 100644 tools/testing/selftests/ftrace/test.d/00basic/mount_options.tc

diff --git a/tools/testing/selftests/ftrace/test.d/00basic/mount_options.tc b/tools/testing/selftests/ftrace/test.d/00basic/mount_options.tc new file mode 100644 index 000000000000..35e8d47d6072 --- /dev/null +++ b/tools/testing/selftests/ftrace/test.d/00basic/mount_options.tc @@ -0,0 +1,101 @@ +#!/bin/sh +# SPDX-License-Identifier: GPL-2.0 +# description: Test tracefs GID mount option +# requires: "[gid=<gid>]":README + +fail() { + local msg="$1" + + echo "FAILED: $msg" + exit_fail +} + +find_alternate_gid() { + local original_gid="$1" + tac /etc/group | grep -v ":$original_gid:" | head -1 | cut -d: -f3 +} + +mount_tracefs_with_options() { + local mount_point="$1" + local options="$2" + + mount -t tracefs -o "$options" nodev "$mount_point" + + setup +} + +unmount_tracefs() { + local mount_point="$1" + + # Need to make sure the mount isn't busy so that we can umount it + (cd $mount_point; finish_ftrace;) + + cleanup +} + +create_instance() { + local mount_point="$1" + local instance="$mount_point/instances/$(mktemp -u test-XXXXXX)" + + mkdir "$instance" + echo "$instance" +} + +remove_instance() { + local instance="$1" + + rmdir "$instance" +} + +check_gid() { + local mount_point="$1" + local expected_gid="$2" + + echo "Checking permission group ..." + + cd "$mount_point" + + for file in "." "events" "events/sched" "events/sched/sched_switch" "events/sched/sched_switch/enable"; do + local gid=`stat -c "%g" $file` + if [ "$gid" -ne "$expected_gid" ]; then + cd - # Return to the previous working directory (tracefs root) + fail "$(realpath $file): Expected group $expected_gid; Got group $gid" + fi + done + + cd - # Return to the previous working directory (tracefs root) +} + +test_gid_mount_option() { + local mount_point=$(get_mount_point) + local mount_options=$(get_mnt_options "$mount_point") + local original_group=$(stat -c "%g" .) + local other_group=$(find_alternate_gid "$original_group") + + # Set up mount options with new GID for testing + local new_options=`echo "$mount_options" | sed -e "s/gid=[0-9]*/gid=$other_group/"` + if [ "$new_options" = "$mount_options" ]; then + new_options="$mount_options,gid=$other_group" + mount_options="$mount_options,gid=$original_group" + fi + + # Unmount existing tracefs instance and mount with new GID + unmount_tracefs "$mount_point" + mount_tracefs_with_options "$mount_point" "$new_options" + + check_gid "$mount_point" "$other_group" + + # Check that files created after the mount inherit the GID + local instance=$(create_instance "$mount_point") + check_gid "$instance" "$other_group" + remove_instance "$instance" + + # Unmount and remount with the original GID + unmount_tracefs "$mount_point" + mount_tracefs_with_options "$mount_point" "$mount_options" + check_gid "$mount_point" "$original_group" +} + +test_gid_mount_option + +exit 0 diff --git a/tools/testing/selftests/ftrace/test.d/00basic/test_ownership.tc b/tools/testing/selftests/ftrace/test.d/00basic/test_ownership.tc index 094419e190c2..e71cc3ad0bdf 100644 --- a/tools/testing/selftests/ftrace/test.d/00basic/test_ownership.tc +++ b/tools/testing/selftests/ftrace/test.d/00basic/test_ownership.tc @@ -1,24 +1,14 @@ #!/bin/sh # SPDX-License-Identifier: GPL-2.0 # description: Test file and directory ownership changes for eventfs +# requires: "[gid=<gid>]":README

original_group=`stat -c "%g" .` original_owner=`stat -c "%u" .`

-mount_point=`stat -c '%m' .` +local mount_point=$(get_mount_point)

-# If stat -c '%m' does not work (e.g. busybox) or failed, try to use the -# current working directory (which should be a tracefs) as the mount point. -if [ ! -d "$mount_point" ]; then - if mount | grep -qw $PWD ; then - mount_point=$PWD - else - # If PWD doesn't work, that is an environmental problem. - exit_unresolved - fi -fi - -mount_options=`mount | grep "$mount_point" | sed -e 's/.*((.*)).*/\1/'` +mount_options=$(get_mnt_options "$mount_point")

# find another owner and group that is not the original other_group=`tac /etc/group | grep -v ":$original_group:" | head -1 | cut -d: -f3` diff --git a/tools/testing/selftests/ftrace/test.d/functions b/tools/testing/selftests/ftrace/test.d/functions index 779f3e62ec90..84d6a9c7ad67 100644 --- a/tools/testing/selftests/ftrace/test.d/functions +++ b/tools/testing/selftests/ftrace/test.d/functions @@ -193,3 +193,28 @@ ftrace_errlog_check() { # err-prefix command-with-error-pos-by-^ command-file # " Command: " and "^\n" => 13 test $(expr 13 + $pos) -eq $N } + +# Helper to get the tracefs mount point +get_mount_point() { + local mount_point=`stat -c '%m' .` + + # If stat -c '%m' does not work (e.g. busybox) or failed, try to use the + # current working directory (which should be a tracefs) as the mount point. + if [ ! -d "$mount_point" ]; then + if mount | grep -qw "$PWD"; then + mount_point=$PWD + else + # If PWD doesn't work, that is an environmental problem. + exit_unresolved + fi + fi + echo "$mount_point" +} + +# Helper function to retrieve mount options for a given mount point +get_mnt_options() { + local mnt_point="$1" + local opts=$(mount | grep -m1 "$mnt_point" | sed -e 's/.*((.*)).*/\1/') + + echo "$opts" +} \ No newline at end of file