On 6/1/2018 1:56 AM, CHANDAN VN wrote: > Hi > > >> On 5/31/2018 9:11 AM, Tejun Heo wrote: >> On Thu, May 31, 2018 at 09:04:25AM -0700, Casey Schaufler wrote: >>>> On 5/31/2018 8:39 AM, Tejun Heo wrote: >>>>> (cc'ing more security folks and copying whole body) >>>>> >>>>> So, I'm sure the patch fixes the memory leak but API wise it looks >>>>> super confusing. Can security folks chime in here? Is this the right >>>>> fix? >>>>> security_inode_getsecctx() provides a security context. Technically, >>>>> this is a data blob, although both provider provide a null terminated >>>>> string. security_inode_getsecurity(), on the other hand, provides a >>>>> string to match an attribute name. The former releases the security >>>>> context with security_release_secctx(), where the later releases the >>>>> string with kfree(). >>>>> >>>>> When the Smack hook smack_inode_getsecctx() was added in 2009 >>>>> for use by labeled NFS the alloc value passed to >>>> smack_inode_getsecurity() was set incorrectly. This wasn't a >>>> major issue, since labeled NFS is a fringe case. When kernfs >>>> started using the hook, it became the issue you discovered. >>>> >>>> The reason that we have all this confusion is that SELinux >>>> generates security contexts as needed, while Smack keeps them >>>> around all the time. Releasing an SELinux context frees memory, >>>> while releasing a Smack context is a null operation. >>> Any chance this detail can be hidden behind security api? This looks >>> pretty error-prone, no? > >>> It *is* hidden behind the security API. The problem is strictly >>> within the Smack code, where the implementer of smack_inode_getsecctx() >>> made an error. > I agree that the fix can be done simply by using "false" for > smack_inode_getsecurity(), but what happens with kernfs_node_setsecdata() > and smack_inode_notifysecctx(). kernfs_node_setsecdata() is probably ignorable > but smack_inode_notifysecctx() is sending the "ctx" to smack_inode_setsecurity() > and since "ctx" would be NULL because we used "false", smack_inode_setsecurity() > becomes dummy. Thank you for pointing this out. You're right, there's more at issue here than changing the alloc flag will fix. I think that calling smack_inode_getsecurity() from smack_inode_getsecctx() is making the code more complicated than it needs to be. I will have a patch shortly. -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
