Each syscall has some arguments and the Linux Audit framework logs each pointer argument as a memory address instead of its values. For instance, when tracking the setxattr syscall, I get its arguments in the following format: "a0":"55f3604ba000" "a1":"7f1b0bd342fd" "a2":"55f3604d9b20" "a3":"38" According to https://man7.org/linux/man-pages/man2/setxattr.2.html, a0 is the file path's starting memory address, a1 is the extended attribute name's starting memory address, a2 is the extended attribute value's starting memory address and a3 is the size in bytes of the extended attribute value. Is it safe to access those memory addresses in order to get their values? I guess not because their content may have been overwritten between the time the syscall log entry was generated by the kernel and the time it's consumed by a Linux Audit client. If indeed it's unsafe to access these memory addresses, is there any other way to get the extended attribute name/value in the setxattr syscall using the Linux Audit framework?

My specific use case: I'm using Auditbeat/Linux Audit to track permission changes done to a disk partition which is mounted by Samba on a Windows Server box. When a Windows user changes permissions of a file in the Samba mount, Linux Audit records a setxattr event and Auditbeat (connected to the kernel's Audit framework via netlink) notifies me of the event. I need to know what permission changes the user has done in the file and AFAIK parsing the ext attrib name/value is the only way to do that.

Thanks in advance.

> They would not be safe to access from userspace after the syscall has > finished. audit records the values of a number of specific syscall > parameters in special records so this would most likely need a new > special record to add to the audit syscall event to record those pointer > contents. AFAIK, that would require a patch to the kernel part of the Linux Audit framework?

> This use case adds and additional challenge. Since this is a filesystem > that is changed remotely, you may not have a record of the remote user > who made the change, but only the server daemon locally that brokered > the change unless that information is in those pointers. I know. The username is not a problem because I have Windows/Linux users mapped with Centrify. If I can get the extended attributes updated on the Linux side, I'm hoping my code can infer the equivalent operations on the Windows side. On Sat, Feb 27, 2021 at 6:44 PM Richard Guy Briggs <rgb(a)redhat.com&gt; wrote: > On 2021-02-26 22:17, Alan Evangelista wrote: > > Each syscall has some arguments and the Linux Audit framework logs each > > pointer argument as a memory address instead of its values. For instance, > > when tracking the setxattr syscall, I get its arguments in the following > > format: > > > > "a0":"55f3604ba000" > > "a1":"7f1b0bd342fd" > > "a2":"55f3604d9b20" > > "a3":"38" > > > > According to https://man7.org/linux/man-pages/man2/setxattr.2.html, a0 > is > > the file path's starting memory address, a1 is the extended attribute > > name's starting memory address, a2 is the extended attribute > > value's starting memory address and a3 is the size in bytes of the > extended > > attribute value. > > > > Is it safe to access those memory addresses in order to get their > values? I > > guess not because their content may have been overwritten between the > time > > the syscall log entry was generated by the kernel and the time it's > > consumed by a Linux Audit client. If indeed it's unsafe to access these > > memory addresses, is there any other way to get the extended attribute > > name/value in the setxattr syscall using the Linux Audit framework? > > They would not be safe to access from userspace after the syscall has > finished. audit records the values of a number of specific syscall > parameters in special records so this would most likely need a new > special record to add to the audit syscall event to record those pointer > contents. > > > My specific use case: I'm using Auditbeat/Linux Audit to track permission > > changes done to a disk partition which is mounted by Samba on a Windows > > Server box. When a Windows user changes permissions of a file in the > Samba > > mount, Linux Audit records a setxattr event and Auditbeat (connected to > the > > kernel's Audit framework via netlink) notifies me of the event. I need to > > know what permission changes the user has done in the file and AFAIK > > parsing the ext attrib name/value is the only way to do that. > > This use case adds and additional challenge. Since this is a filesystem > that is changed remotely, you may not have a record of the remote user > who made the change, but only the server daemon locally that brokered > the change unless that information is in those pointers. > > > Thanks in advance. > > - RGB