On 12/8/20 10:03 PM, Dmitry Vyukov wrote: > On Wed, Dec 9, 2020 at 12:15 AM Randy Dunlap <rdunlap@xxxxxxxxxxxxx> wrote: >> >> On 12/8/20 2:54 PM, David Howells wrote: >>> Randy Dunlap <rdunlap@xxxxxxxxxxxxx> wrote: >>> >>>>> Now the backtrace only shows what the state was when the string was allocated; >>>>> it doesn't show what happened to it after that, so another possibility is that >>>>> the filesystem being mounted nicked what vfs_parse_fs_param() had rightfully >>>>> stolen, transferring fc->source somewhere else and then failed to release it - >>>>> most likely on mount failure (ie. it's an error handling bug in the >>>>> filesystem). >>>>> >>>>> Do we know what filesystem it was? >>>> >>>> Yes, it's call AFS (or kAFS). >>> >>> Hmmm... afs parses the string in afs_parse_source() without modifying it, >>> then moves the pointer to fc->source (parallelling vfs_parse_fs_param()) and >>> doesn't touch it again. fc->source should be cleaned up by do_new_mount() >>> calling put_fs_context() at the end of the function. >>> >>> As far as I can tell with the attached print-insertion patch, it works, called >>> by the following commands, some of which are correct and some which aren't: >>> >>> # mount -t afs none /xfstest.test/ -o dyn >>> # umount /xfstest.test >>> # mount -t afs "" /xfstest.test/ -o foo >>> mount: /xfstest.test: bad option; for several filesystems (e.g. nfs, cifs) you might need a /sbin/mount.<type> helper program. >>> # umount /xfstest.test >>> umount: /xfstest.test: not mounted. >>> # mount -t afs %xfstest.test20 /xfstest.test/ -o foo >>> mount: /xfstest.test: bad option; for several filesystems (e.g. nfs, cifs) you might need a /sbin/mount.<type> helper program. >>> # umount /xfstest.test >>> umount: /xfstest.test: not mounted. >>> # mount -t afs %xfstest.test20 /xfstest.test/ >>> # umount /xfstest.test >>> >>> Do you know if the mount was successful and what the mount parameters were? >> >> Here's the syzbot reproducer: >> https://syzkaller.appspot.com/x/repro.c?x=129ca3d6500000 >> >> The "interesting" mount params are: >> source=%^]$[+%](${:\017k[)-:,source=%^]$[+.](%{:\017\200[)-:,\000 >> >> There is no other AFS activity: nothing mounted, no cells known (or >> whatever that is), etc. >> >> I don't recall if the mount was successful and I can't test it just now. >> My laptop is mucked up. >> >> >> Be aware that this report could just be a false positive: it waits >> for 5 seconds then looks for a memleak. AFAIK, it's possible that the "leaked" >> memory is still in valid use and will be freed some day. > > FWIW KMEMLEAK scans memory for pointers. If it claims a memory leak, > it means the heap object is not referenced anywhere anymore. There are > no live pointers to it to call kfree or anything else. > Some false positives are theoretically possible, but so I don't > remember any, all reported ones were true leaks: > https://syzkaller.appspot.com/upstream/fixed?manager=ci-upstream-gce-leak > OK, great, thanks for the info. > > >>> David >>> --- >>> diff --git a/fs/afs/super.c b/fs/afs/super.c >>> index 6c5900df6aa5..4c44ec0196c9 100644 >>> --- a/fs/afs/super.c >>> +++ b/fs/afs/super.c >>> @@ -299,7 +299,7 @@ static int afs_parse_source(struct fs_context *fc, struct fs_parameter *param) >>> ctx->cell = cell; >>> } >>> >>> - _debug("CELL:%s [%p] VOLUME:%*.*s SUFFIX:%s TYPE:%d%s", >>> + kdebug("CELL:%s [%p] VOLUME:%*.*s SUFFIX:%s TYPE:%d%s", >>> ctx->cell->name, ctx->cell, >>> ctx->volnamesz, ctx->volnamesz, ctx->volname, >>> suffix ?: "-", ctx->type, ctx->force ? " FORCE" : ""); >>> @@ -318,6 +318,8 @@ static int afs_parse_param(struct fs_context *fc, struct fs_parameter *param) >>> struct afs_fs_context *ctx = fc->fs_private; >>> int opt; >>> >>> + kenter("%s,%p '%s'", param->key, param->string, param->string); >>> + >>> opt = fs_parse(fc, afs_fs_parameters, param, &result); >>> if (opt < 0) >>> return opt; >>> diff --git a/fs/fs_context.c b/fs/fs_context.c >>> index 2834d1afa6e8..f530a33876ce 100644 >>> --- a/fs/fs_context.c >>> +++ b/fs/fs_context.c >>> @@ -450,6 +450,8 @@ void put_fs_context(struct fs_context *fc) >>> put_user_ns(fc->user_ns); >>> put_cred(fc->cred); >>> put_fc_log(fc); >>> + if (strcmp(fc->fs_type->name, "afs") == 0) >>> + printk("PUT %p '%s'\n", fc->source, fc->source); >>> put_filesystem(fc->fs_type); >>> kfree(fc->source); >>> kfree(fc); >>> @@ -671,6 +673,8 @@ void vfs_clean_context(struct fs_context *fc) >>> fc->s_fs_info = NULL; >>> fc->sb_flags = 0; >>> security_free_mnt_opts(&fc->security); >>> + if (strcmp(fc->fs_type->name, "afs") == 0) >>> + printk("CLEAN %p '%s'\n", fc->source, fc->source); >>> kfree(fc->source); >>> fc->source = NULL; >>> >>> >> >> I'll check more after my test machine is working again. >> >> thanks. >> -- >> ~Randy >> >> -- >> You received this message because you are subscribed to the Google Groups "syzkaller-bugs" group. >> To unsubscribe from this group and stop receiving emails from it, send an email to syzkaller-bugs+unsubscribe@xxxxxxxxxxxxxxxx. >> To view this discussion on the web visit https://groups.google.com/d/msgid/syzkaller-bugs/e6d9fd7e-ea43-25a6-9f1e-16a605de0f2d%40infradead.org. -- ~Randy
