Messages in this thread | | | From | Song Liu <> | Subject | Re: [PATCH v2] tracing: fix bad use of igrab in trace_uprobe.c | Date | Thu, 19 Apr 2018 16:37:08 +0000 |
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> On Apr 19, 2018, at 7:44 AM, Miklos Szeredi <miklos@szeredi.hu> wrote: > > On Thu, Apr 19, 2018 at 10:58 AM, Miklos Szeredi <miklos@szeredi.hu> wrote: >> On Wed, Apr 18, 2018 at 7:40 PM, Song Liu <songliubraving@fb.com> wrote: >>> As Miklos reported and suggested: >>> >>> This pattern repeats two times in trace_uprobe.c and in >>> kernel/events/core.c as well: >>> >>> ret = kern_path(filename, LOOKUP_FOLLOW, &path); >>> if (ret) >>> goto fail_address_parse; >>> >>> inode = igrab(d_inode(path.dentry)); >>> path_put(&path); >>> >>> And it's wrong. You can only hold a reference to the inode if you >>> have an active ref to the superblock as well (which is normally >>> through path.mnt) or holding s_umount. >>> >>> This way unmounting the containing filesystem while the tracepoint is >>> active will give you the "VFS: Busy inodes after unmount..." message >>> and a crash when the inode is finally put. >>> >>> Solution: store path instead of inode. >>> >>> This patch fixes two instances in trace_uprobe.c. >>> >>> Fixes: f3f096cfedf8 ("tracing: Provide trace events interface for uprobes") >>> Fixes: 33ea4b24277b ("perf/core: Implement the 'perf_uprobe' PMU") >>> Cc: Steven Rostedt <rostedt@goodmis.org> >>> Cc: Ingo Molnar <mingo@redhat.com> >>> Cc: Howard McLauchlan <hmclauchlan@fb.com> >>> Cc: Josef Bacik <jbacik@fb.com> >>> Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com> >>> Reported-by: Miklos Szeredi <miklos@szeredi.hu> >>> Signed-off-by: Song Liu <songliubraving@fb.com> >>> --- >>> kernel/trace/trace_uprobe.c | 49 +++++++++++++++------------------------------ >>> 1 file changed, 16 insertions(+), 33 deletions(-) >>> >>> diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c >>> index 34fd0e0..d9ee522c 100644 >>> --- a/kernel/trace/trace_uprobe.c >>> +++ b/kernel/trace/trace_uprobe.c >>> @@ -55,7 +55,7 @@ struct trace_uprobe { >>> struct list_head list; >>> struct trace_uprobe_filter filter; >>> struct uprobe_consumer consumer; >>> - struct inode *inode; >>> + struct path path; >>> char *filename; >>> unsigned long offset; >>> unsigned long nhit; >>> @@ -289,7 +289,7 @@ static void free_trace_uprobe(struct trace_uprobe *tu) >>> for (i = 0; i < tu->tp.nr_args; i++) >>> traceprobe_free_probe_arg(&tu->tp.args[i]); >>> >>> - iput(tu->inode); >>> + path_put(&tu->path); >>> kfree(tu->tp.call.class->system); >>> kfree(tu->tp.call.name); >>> kfree(tu->filename); >>> @@ -363,7 +363,6 @@ static int register_trace_uprobe(struct trace_uprobe *tu) >>> static int create_trace_uprobe(int argc, char **argv) >>> { >>> struct trace_uprobe *tu; >>> - struct inode *inode; >>> char *arg, *event, *group, *filename; >>> char buf[MAX_EVENT_NAME_LEN]; >>> struct path path; >>> @@ -371,7 +370,6 @@ static int create_trace_uprobe(int argc, char **argv) >>> bool is_delete, is_return; >>> int i, ret; >>> >>> - inode = NULL; >>> ret = 0; >>> is_delete = false; >>> is_return = false; >>> @@ -437,24 +435,14 @@ static int create_trace_uprobe(int argc, char **argv) >>> } >>> /* Find the last occurrence, in case the path contains ':' too. */ >>> arg = strrchr(argv[1], ':'); >>> - if (!arg) { >>> - ret = -EINVAL; >>> - goto fail_address_parse; >>> - } >>> + if (!arg) >>> + return -EINVAL; >>> >>> *arg++ = '\0'; >>> filename = argv[1]; >>> ret = kern_path(filename, LOOKUP_FOLLOW, &path); >>> if (ret) >>> - goto fail_address_parse; >>> - >>> - inode = igrab(d_real_inode(path.dentry)); > > Also, where has the d_real_inode() gone? > > Looks like we need tu->inode back, since the return value of > d_real_inode() may change over time. I'd do the "tu->inode = > d_real_inode(tu->path.dentry)" just before first use (i.e. when > enabling the tracepoint). > > Thanks, > Miklos >
Do we need mechanism to prevent the return value of d_real_inode() to change? Would the following sequence happen?
create trace_uprobe enable trace_uprobe (uprobe_register) d_real changes disable trace_uprobe (uprobe_unregister get wrong inode?)
Another case might be:
create trace_uprobe enable trace_uprobe (uprobe_register) disable trace_uprobe (uprobe_unregister) d_real changes enable trace_uprobe (do we need new inode for uprobe_register)
Thanks, Song
> >>> - path_put(&path); >>> - >>> - if (!inode || !S_ISREG(inode->i_mode)) { >> >> Where has the S_ISREG check gone? >> >>> - ret = -EINVAL; >>> - goto fail_address_parse; >>> - } >>> + return ret; >>> >>> ret = kstrtoul(arg, 0, &offset); >>> if (ret) >>> @@ -490,7 +478,7 @@ static int create_trace_uprobe(int argc, char **argv) >>> goto fail_address_parse; >>> } >>> tu->offset = offset; >>> - tu->inode = inode; >>> + tu->path = path; >>> tu->filename = kstrdup(filename, GFP_KERNEL); >>> >>> if (!tu->filename) { >>> @@ -558,7 +546,7 @@ static int create_trace_uprobe(int argc, char **argv) >>> return ret; >>> >>> fail_address_parse: >>> - iput(inode); >>> + path_put(&path); >>> >>> pr_info("Failed to parse address or file.\n"); >>> >>> @@ -922,7 +910,8 @@ probe_event_enable(struct trace_uprobe *tu, struct trace_event_file *file, >>> goto err_flags; >>> >>> tu->consumer.filter = filter; >>> - ret = uprobe_register(tu->inode, tu->offset, &tu->consumer); >>> + ret = uprobe_register(d_inode(tu->path.dentry), tu->offset, >>> + &tu->consumer); >>> if (ret) >>> goto err_buffer; >>> >>> @@ -966,7 +955,7 @@ probe_event_disable(struct trace_uprobe *tu, struct trace_event_file *file) >>> >>> WARN_ON(!uprobe_filter_is_empty(&tu->filter)); >>> >>> - uprobe_unregister(tu->inode, tu->offset, &tu->consumer); >>> + uprobe_unregister(d_inode(tu->path.dentry), tu->offset, &tu->consumer); >>> tu->tp.flags &= file ? ~TP_FLAG_TRACE : ~TP_FLAG_PROFILE; >>> >>> uprobe_buffer_disable(); >>> @@ -1041,7 +1030,8 @@ static int uprobe_perf_close(struct trace_uprobe *tu, struct perf_event *event) >>> write_unlock(&tu->filter.rwlock); >>> >>> if (!done) >>> - return uprobe_apply(tu->inode, tu->offset, &tu->consumer, false); >>> + return uprobe_apply(d_inode(tu->path.dentry), tu->offset, >>> + &tu->consumer, false); >>> >>> return 0; >>> } >>> @@ -1073,7 +1063,8 @@ static int uprobe_perf_open(struct trace_uprobe *tu, struct perf_event *event) >>> >>> err = 0; >>> if (!done) { >>> - err = uprobe_apply(tu->inode, tu->offset, &tu->consumer, true); >>> + err = uprobe_apply(d_inode(tu->path.dentry), >>> + tu->offset, &tu->consumer, true); >>> if (err) >>> uprobe_perf_close(tu, event); >>> } >>> @@ -1337,7 +1328,6 @@ struct trace_event_call * >>> create_local_trace_uprobe(char *name, unsigned long offs, bool is_return) >>> { >>> struct trace_uprobe *tu; >>> - struct inode *inode; >>> struct path path; >>> int ret; >>> >>> @@ -1345,14 +1335,6 @@ create_local_trace_uprobe(char *name, unsigned long offs, bool is_return) >>> if (ret) >>> return ERR_PTR(ret); >>> >>> - inode = igrab(d_inode(path.dentry)); >>> - path_put(&path); >>> - >>> - if (!inode || !S_ISREG(inode->i_mode)) { >> >> And here, again. >> >> Otherwise ACK. >> >> Also please create a separate patch that removes igrab/iput calls from >> kernel/events/uprobes.c and adds a comment to the effect that the >> caller is required to keep the inode (and the containing mount) >> referenced. >> >> Thanks, >> Miklos
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