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Howlett" , Alice Ryhl , Andrew Ballance , Josh Law , maple-tree@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/3] lib/maple_tree: fix potential NULL dereference in mas_pop_node() Message-Id: <20260312134531.49c1f9171b4b0bc8352e678d@linux-foundation.org> In-Reply-To: <20260312184054.23481-1-objecting@objecting.org> References: <20260312184054.23481-1-objecting@objecting.org> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 38A0520011 X-Stat-Signature: ckj59wg57ahxxunytq5ccijr8ik38e3g X-Rspam-User: X-HE-Tag: 1773348333-739584 X-HE-Meta: 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 Eau9qnzj 3TfPUaYEhtqW7zLRcqnsD91reP7FquY3HE9Nb0M+pYEHwLkv+al3tqpzE4ns6555LBEdECGmMqvh2gZVpPK7u7iBr42Y/mzqMvHRrzFH+BHD6b4Bh1GWhuPdcHHBGaJwUFpx+5uC71TsjGjIWer+pf6kdELfwGGFM2GOpigVpuO8PnQMonEbMYnIwpNAHhJi+dDuI0VUymh833wbbl+VoqkKrSXq1Hlkaz+gSGp4L1+SvhBgggPMA2S9SpUnfU5LYLfJRskANbZiITe/HLYu52VDfSHnpBWQ+pAtmvQRl6tyBECFiYI0Rzctvth4XxD+xsjAl3Lipe/bcRQjBvij0+t4kpsxTBETTOPVYqOJB2R7w4ygfbquzi3YKNGXI5Je931Pe Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, 12 Mar 2026 18:40:53 +0000 Josh Law wrote: > If kmem_cache_alloc_from_sheaf() returns NULL (possible under > GFP_NOWAIT pressure), mas_pop_node() falls through to the out label > and dereferences the NULL pointer in memset(ret, 0, sizeof(*ret)). This is such a glaring bug that I wonder if we're missing something. > Add a WARN_ON_ONCE NULL check after the sheaf allocation to bail out > early, matching the existing pattern for the !mas->sheaf case above. > > Signed-off-by: Josh Law > --- > lib/maple_tree.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/lib/maple_tree.c b/lib/maple_tree.c > index 739918e859e5..87a2ba6468ca 100644 > --- a/lib/maple_tree.c > +++ b/lib/maple_tree.c > @@ -1063,6 +1063,8 @@ static __always_inline struct maple_node *mas_pop_node(struct ma_state *mas) > return NULL; > > ret = kmem_cache_alloc_from_sheaf(maple_node_cache, GFP_NOWAIT, mas->sheaf); > + if (WARN_ON_ONCE(!ret)) > + return NULL; If we're going to do this then we may as well restore !__GFP_NOWARN, get more relevant information. But a GFP_NOWAIT allocation attempt can fail relatively easily so callers must be equipped to handle it - perhaps no need for any warning.