| Message ID | 20231130201222.3613535-3-keescook@chromium.org (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | kernfs: Convert from strlcpy() to strscpy() | expand |
| Context | Check | Description |
|---|---|---|
| netdev/tree_selection | success | Not a local patch |
Le 30/11/2023 à 21:12, Kees Cook a écrit : > One of the last remaining users of strlcpy() in the kernel is > kernfs_path_from_node_locked(), which passes back the problematic "length > we _would_ have copied" return value to indicate truncation. Convert the > chain of all callers to use the negative return value (some of which > already doing this explicitly). All callers were already also checking > for negative return values, so the risk to missed checks looks very low. > > In this analysis, it was found that cgroup1_release_agent() actually > didn't handle the "too large" condition, so this is technically also a > bug fix. :) > > Here's the chain of callers, and resolution identifying each one as now > handling the correct return value: > > kernfs_path_from_node_locked() > kernfs_path_from_node() > pr_cont_kernfs_path() > returns void > kernfs_path() > sysfs_warn_dup() > return value ignored > cgroup_path() > blkg_path() > bfq_bic_update_cgroup() > return value ignored > TRACE_IOCG_PATH() > return value ignored > TRACE_CGROUP_PATH() > return value ignored > perf_event_cgroup() > return value ignored > task_group_path() > return value ignored > damon_sysfs_memcg_path_eq() > return value ignored > get_mm_memcg_path() > return value ignored > lru_gen_seq_show() > return value ignored > cgroup_path_from_kernfs_id() > return value ignored > cgroup_show_path() > already converted "too large" error to negative value > cgroup_path_ns_locked() > cgroup_path_ns() > bpf_iter_cgroup_show_fdinfo() > return value ignored > cgroup1_release_agent() > wasn't checking "too large" error > proc_cgroup_show() > already converted "too large" to negative value > > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> > Cc: Tejun Heo <tj@kernel.org> > Cc: Zefan Li <lizefan.x@bytedance.com> > Cc: Johannes Weiner <hannes@cmpxchg.org> > Cc: Waiman Long <longman@redhat.com> > Cc: cgroups@vger.kernel.org > Co-developed-by: Azeem Shaikh <azeemshaikh38@gmail.com> > Signed-off-by: Azeem Shaikh <azeemshaikh38@gmail.com> > Link: https://lore.kernel.org/r/20231116192127.1558276-3-keescook@chromium.org > Signed-off-by: Kees Cook <keescook@chromium.org> > --- > fs/kernfs/dir.c | 37 ++++++++++++++++++++----------------- > kernel/cgroup/cgroup-v1.c | 2 +- > kernel/cgroup/cgroup.c | 4 ++-- > kernel/cgroup/cpuset.c | 2 +- > 4 files changed, 24 insertions(+), 21 deletions(-) > > diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c > index 8c0e5442597e..183f353b3852 100644 > --- a/fs/kernfs/dir.c > +++ b/fs/kernfs/dir.c > @@ -127,7 +127,7 @@ static struct kernfs_node *kernfs_common_ancestor(struct kernfs_node *a, > * > * [3] when @kn_to is %NULL result will be "(null)" > * > - * Return: the length of the full path. If the full length is equal to or > + * Return: the length of the constructed path. If the path would have been > * greater than @buflen, @buf contains the truncated path with the trailing > * '\0'. On error, -errno is returned. > */ > @@ -138,16 +138,17 @@ static int kernfs_path_from_node_locked(struct kernfs_node *kn_to, > struct kernfs_node *kn, *common; > const char parent_str[] = "/.."; > size_t depth_from, depth_to, len = 0; > + ssize_t copied; > int i, j; > > if (!kn_to) > - return strlcpy(buf, "(null)", buflen); > + return strscpy(buf, "(null)", buflen); > > if (!kn_from) > kn_from = kernfs_root(kn_to)->kn; > > if (kn_from == kn_to) > - return strlcpy(buf, "/", buflen); > + return strscpy(buf, "/", buflen); > > common = kernfs_common_ancestor(kn_from, kn_to); > if (WARN_ON(!common)) > @@ -158,18 +159,22 @@ static int kernfs_path_from_node_locked(struct kernfs_node *kn_to, > > buf[0] = '\0'; > > - for (i = 0; i < depth_from; i++) > - len += strlcpy(buf + len, parent_str, > - len < buflen ? buflen - len : 0); > + for (i = 0; i < depth_from; i++) { > + copied = strscpy(buf + len, parent_str, buflen - len); > + if (copied < 0) > + return copied; > + len += copied; > + } > > /* Calculate how many bytes we need for the rest */ > for (i = depth_to - 1; i >= 0; i--) { > for (kn = kn_to, j = 0; j < i; j++) > kn = kn->parent; > - len += strlcpy(buf + len, "/", > - len < buflen ? buflen - len : 0); > - len += strlcpy(buf + len, kn->name, > - len < buflen ? buflen - len : 0); > + > + copied = scnprintf(buf + len, buflen - len, "/%s", kn->name); > + if (copied < 0) Can scnprintf() return <0 ? > + return copied; > + len += copied; > } ...
On Thu, Nov 30, 2023 at 09:38:11PM +0100, Christophe JAILLET wrote: > Le 30/11/2023 à 21:12, Kees Cook a écrit : > [...] > > diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c > > index 8c0e5442597e..183f353b3852 100644 > > --- a/fs/kernfs/dir.c > > +++ b/fs/kernfs/dir.c > [...] > > @@ -158,18 +159,22 @@ static int kernfs_path_from_node_locked(struct kernfs_node *kn_to, > > buf[0] = '\0'; > > - for (i = 0; i < depth_from; i++) > > - len += strlcpy(buf + len, parent_str, > > - len < buflen ? buflen - len : 0); > > + for (i = 0; i < depth_from; i++) { > > + copied = strscpy(buf + len, parent_str, buflen - len); > > + if (copied < 0) > > + return copied; > > + len += copied; > > + } > > /* Calculate how many bytes we need for the rest */ > > for (i = depth_to - 1; i >= 0; i--) { > > for (kn = kn_to, j = 0; j < i; j++) > > kn = kn->parent; > > - len += strlcpy(buf + len, "/", > > - len < buflen ? buflen - len : 0); > > - len += strlcpy(buf + len, kn->name, > > - len < buflen ? buflen - len : 0); > > + > > + copied = scnprintf(buf + len, buflen - len, "/%s", kn->name); > > + if (copied < 0) > > Can scnprintf() return <0 ? Ah, yeah, it's can't at all[1]. I forgot! :) Honestly, that function should return size_t, not int... I will send a v3 with this adjusted, but I'll wait for more review... Thanks! -Kees [1] https://docs.kernel.org/core-api/kernel-api.html#c.scnprintf
diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c index 8c0e5442597e..183f353b3852 100644 --- a/fs/kernfs/dir.c +++ b/fs/kernfs/dir.c @@ -127,7 +127,7 @@ static struct kernfs_node *kernfs_common_ancestor(struct kernfs_node *a, * * [3] when @kn_to is %NULL result will be "(null)" * - * Return: the length of the full path. If the full length is equal to or + * Return: the length of the constructed path. If the path would have been * greater than @buflen, @buf contains the truncated path with the trailing * '\0'. On error, -errno is returned. */ @@ -138,16 +138,17 @@ static int kernfs_path_from_node_locked(struct kernfs_node *kn_to, struct kernfs_node *kn, *common; const char parent_str[] = "/.."; size_t depth_from, depth_to, len = 0; + ssize_t copied; int i, j; if (!kn_to) - return strlcpy(buf, "(null)", buflen); + return strscpy(buf, "(null)", buflen); if (!kn_from) kn_from = kernfs_root(kn_to)->kn; if (kn_from == kn_to) - return strlcpy(buf, "/", buflen); + return strscpy(buf, "/", buflen); common = kernfs_common_ancestor(kn_from, kn_to); if (WARN_ON(!common)) @@ -158,18 +159,22 @@ static int kernfs_path_from_node_locked(struct kernfs_node *kn_to, buf[0] = '\0'; - for (i = 0; i < depth_from; i++) - len += strlcpy(buf + len, parent_str, - len < buflen ? buflen - len : 0); + for (i = 0; i < depth_from; i++) { + copied = strscpy(buf + len, parent_str, buflen - len); + if (copied < 0) + return copied; + len += copied; + } /* Calculate how many bytes we need for the rest */ for (i = depth_to - 1; i >= 0; i--) { for (kn = kn_to, j = 0; j < i; j++) kn = kn->parent; - len += strlcpy(buf + len, "/", - len < buflen ? buflen - len : 0); - len += strlcpy(buf + len, kn->name, - len < buflen ? buflen - len : 0); + + copied = scnprintf(buf + len, buflen - len, "/%s", kn->name); + if (copied < 0) + return copied; + len += copied; } return len; @@ -214,7 +219,7 @@ int kernfs_name(struct kernfs_node *kn, char *buf, size_t buflen) * path (which includes '..'s) as needed to reach from @from to @to is * returned. * - * Return: the length of the full path. If the full length is equal to or + * Return: the length of the constructed path. If the path would have been * greater than @buflen, @buf contains the truncated path with the trailing * '\0'. On error, -errno is returned. */ @@ -265,12 +270,10 @@ void pr_cont_kernfs_path(struct kernfs_node *kn) sz = kernfs_path_from_node(kn, NULL, kernfs_pr_cont_buf, sizeof(kernfs_pr_cont_buf)); if (sz < 0) { - pr_cont("(error)"); - goto out; - } - - if (sz >= sizeof(kernfs_pr_cont_buf)) { - pr_cont("(name too long)"); + if (sz == -E2BIG) + pr_cont("(name too long)"); + else + pr_cont("(error)"); goto out; } diff --git a/kernel/cgroup/cgroup-v1.c b/kernel/cgroup/cgroup-v1.c index 76db6c67e39a..9cb00ebe9ac6 100644 --- a/kernel/cgroup/cgroup-v1.c +++ b/kernel/cgroup/cgroup-v1.c @@ -802,7 +802,7 @@ void cgroup1_release_agent(struct work_struct *work) goto out_free; ret = cgroup_path_ns(cgrp, pathbuf, PATH_MAX, &init_cgroup_ns); - if (ret < 0 || ret >= PATH_MAX) + if (ret < 0) goto out_free; argv[0] = agentbuf; diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c index 4b9ff41ca603..8d2674c6aaef 100644 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -1893,7 +1893,7 @@ int cgroup_show_path(struct seq_file *sf, struct kernfs_node *kf_node, len = kernfs_path_from_node(kf_node, ns_cgroup->kn, buf, PATH_MAX); spin_unlock_irq(&css_set_lock); - if (len >= PATH_MAX) + if (len == -E2BIG) len = -ERANGE; else if (len > 0) { seq_escape(sf, buf, " \t\n\\"); @@ -6301,7 +6301,7 @@ int proc_cgroup_show(struct seq_file *m, struct pid_namespace *ns, if (cgroup_on_dfl(cgrp) || !(tsk->flags & PF_EXITING)) { retval = cgroup_path_ns_locked(cgrp, buf, PATH_MAX, current->nsproxy->cgroup_ns); - if (retval >= PATH_MAX) + if (retval == -E2BIG) retval = -ENAMETOOLONG; if (retval < 0) goto out_unlock; diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c index 615daaf87f1f..fb29158ae825 100644 --- a/kernel/cgroup/cpuset.c +++ b/kernel/cgroup/cpuset.c @@ -4941,7 +4941,7 @@ int proc_cpuset_show(struct seq_file *m, struct pid_namespace *ns, retval = cgroup_path_ns(css->cgroup, buf, PATH_MAX, current->nsproxy->cgroup_ns); css_put(css); - if (retval >= PATH_MAX) + if (retval == -E2BIG) retval = -ENAMETOOLONG; if (retval < 0) goto out_free;
One of the last remaining users of strlcpy() in the kernel is kernfs_path_from_node_locked(), which passes back the problematic "length we _would_ have copied" return value to indicate truncation. Convert the chain of all callers to use the negative return value (some of which already doing this explicitly). All callers were already also checking for negative return values, so the risk to missed checks looks very low. In this analysis, it was found that cgroup1_release_agent() actually didn't handle the "too large" condition, so this is technically also a bug fix. :) Here's the chain of callers, and resolution identifying each one as now handling the correct return value: kernfs_path_from_node_locked() kernfs_path_from_node() pr_cont_kernfs_path() returns void kernfs_path() sysfs_warn_dup() return value ignored cgroup_path() blkg_path() bfq_bic_update_cgroup() return value ignored TRACE_IOCG_PATH() return value ignored TRACE_CGROUP_PATH() return value ignored perf_event_cgroup() return value ignored task_group_path() return value ignored damon_sysfs_memcg_path_eq() return value ignored get_mm_memcg_path() return value ignored lru_gen_seq_show() return value ignored cgroup_path_from_kernfs_id() return value ignored cgroup_show_path() already converted "too large" error to negative value cgroup_path_ns_locked() cgroup_path_ns() bpf_iter_cgroup_show_fdinfo() return value ignored cgroup1_release_agent() wasn't checking "too large" error proc_cgroup_show() already converted "too large" to negative value Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Tejun Heo <tj@kernel.org> Cc: Zefan Li <lizefan.x@bytedance.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Waiman Long <longman@redhat.com> Cc: cgroups@vger.kernel.org Co-developed-by: Azeem Shaikh <azeemshaikh38@gmail.com> Signed-off-by: Azeem Shaikh <azeemshaikh38@gmail.com> Link: https://lore.kernel.org/r/20231116192127.1558276-3-keescook@chromium.org Signed-off-by: Kees Cook <keescook@chromium.org> --- fs/kernfs/dir.c | 37 ++++++++++++++++++++----------------- kernel/cgroup/cgroup-v1.c | 2 +- kernel/cgroup/cgroup.c | 4 ++-- kernel/cgroup/cpuset.c | 2 +- 4 files changed, 24 insertions(+), 21 deletions(-)