[PATCH v2 0/1] virt-aa-helper: Avoid duplicate when append rule
when a device is dynamically attached to a VM, and it needs a special system access for apparmor, libvirt calls virt-aa-helper (with argument -F) to append a new rule to the apparmor profile of the VM. virt-aa-helper does not check for duplicate and blindly appends the rule to the profile. since there is no rule removal when a device is detached, this can make the profile grow in size if a big number of attach/detach operations are done and the profile might hit the size limit and futur attach operations might dysfunction because no rule can be added into the apparmor profile. this patch tries to mitigate this issue by doing a duplicate check when rules are appended into the profile. this fix does not guarantee the absence of duplicates but should be enough to prevent the profile to grow significantly in size and reach its size limit. This v2 takes into account the feedback from Michal Prívozník for the original submission: https://lists.libvirt.org/archives/list/devel@lists.libvirt.org/thread/2HIZC... v2: - early exit if duplicate is detected - improve the check condition for existing profile data Hector Cao (1): virt-aa-helper: Avoid duplicate when append rule src/security/virt-aa-helper.c | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-) -- 2.34.1
From: Hector Cao <hector.cao@canonical.com> when a device is dynamically attached to a VM, and it needs a special system access for apparmor, libvirt calls virt-aa-helper (with argument -F) to append a new rule to the apparmor profile of the VM. virt-aa-helper does not check for duplicate and blindly appends the rule to the profile. since there is no rule removal when a device is detached, this can make the profile grow in size if a big number of attach/detach operations are done and the profile might hit the size limit and futur attach operations might dysfunction because no rule can be added into the apparmor profile. this patch tries to mitigate this issue by doing a duplicate check when rules are appended into the profile. this fix does not guarantee the absence of duplicates but should be enough to prevent the profile to grow significantly in size and reach its size limit. Signed-off-by: Hector CAO <hector.cao@canonical.com> --- src/security/virt-aa-helper.c | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-) diff --git a/src/security/virt-aa-helper.c b/src/security/virt-aa-helper.c index b662d971cb..63d5f48025 100644 --- a/src/security/virt-aa-helper.c +++ b/src/security/virt-aa-helper.c @@ -208,10 +208,21 @@ update_include_file(const char *include_file, const char *included_files, return -1; } - if (append && virFileExists(include_file)) + if (append && existing) { + /* duplicate check: include_files might contain multiple rules + * the best is to check for each rule (separated by \n) but + * it might be overkilled, just do the check for the whole + * include_files. + * most of the time, include_files contains only one rule + * so this check is ok to avoid the overflow of the profile + * duplicates might still exist though. + */ + if (strstr(existing, included_files) != NULL) + return 0; pcontent = g_strdup_printf("%s%s", existing, included_files); - else + } else { pcontent = g_strdup_printf("%s%s", warning, included_files); + } plen = strlen(pcontent); if (plen > MAX_FILE_LEN) { -- 2.34.1
On 8/20/25 17:49, Hector CAO wrote:
From: Hector Cao <hector.cao@canonical.com>
when a device is dynamically attached to a VM, and it needs a special system access for apparmor, libvirt calls virt-aa-helper (with argument -F) to append a new rule to the apparmor profile of the VM. virt-aa-helper does not check for duplicate and blindly appends the rule to the profile. since there is no rule removal when a device is detached, this can make the profile grow in size if a big number of attach/detach operations are done and the profile might hit the size limit and futur attach operations might dysfunction because no rule can be added into the apparmor profile.
this patch tries to mitigate this issue by doing a duplicate check when rules are appended into the profile. this fix does not guarantee the absence of duplicates but should be enough to prevent the profile to grow significantly in size and reach its size limit.
Signed-off-by: Hector CAO <hector.cao@canonical.com> --- src/security/virt-aa-helper.c | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-)
Reviewed-by: Michal Privoznik <mprivozn@redhat.com> and merged. Congratulations on your first libvirt contribution! Michal
participants (2)
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Hector CAO -
Michal Prívozník