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charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: F29B4C0004 X-Stat-Signature: 3ydyt9scupzi8xzjg5fg4qdoi4u1wj9u X-HE-Tag: 1746064656-384716 X-HE-Meta: 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 ZEzR9Dex bVdOai3IEi97VoMoomynvH5Nm6z1Rh6yXD7BMHbOUk9iQzLL4KLHefGVQAHQ3SmmrXw23Hlnw1P+NDsYCLmKrrwKIdKGVy+njHkqwp3+MOUwNq4NWju6hYnoVXQIA2Sx5GI8NClwpW0lwbMmjY+fwjDoSMxb7Pabu6BUGKrGURlB07Bc5lNCteEzCgRFgxBIEwNrW7E9+zqTP0Nhq9t/3aDrb/yPfo10dbyeEfYLAsh8eMj2kLhrFxnsMKOOf8dEtP/d7CuqVffVniwBFjivzyARgMXVTvEeUrD528zdUkKEqmsRexL9x/F8Idx9ZvPvymIvJU8SaSdelcS70XPBEzniOIQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi Dan On Wed, Apr 30, 2025 at 3:59=E2=80=AFPM Dan Carpenter wrote: > > On Wed, Apr 09, 2025 at 03:06:19PM +0800, Zhongkun He wrote: > > + /* set by userspace for anonymous memory only */ > > + if (!strncmp("max", swap_string, sizeof("max"))) { > > This pattern of strncmp("foo", str, sizeof("foo")) is exactly the same > as strcmp(). It doesn't provide any additional security. The strncmp() > function is meant for matching string prefixes and it's a relatively > common bug to do this: > > intended: if (strcmp(string, "prefix", sizeof("prefix") - 1) =3D=3D 0) { > actual: if (strcmp(string, "prefix", sizeof("prefix")) =3D=3D 0) { > Yes, I understand the difference. > I have a static checker warning for these: > https://lore.kernel.org/all/30210ed77b40b4b6629de659cb56b9ec7832c447.1744= 452787.git.dan.carpenter@linaro.org/ > > If people deliberately misuse the function then it makes it trickier > to tell accidental mistakes from deliberate mistakes. > if (!strncmp("max", swap_string, sizeof("max"))) { The length of swap_string is 5 because it's read using sscanf, which will add the null terminator \0 at the end of the string. If we input max into the interface, swap_string will contain max\0, which is equivalent to the string "max". Since we only need to compare the first few characters(There are other possible inputs as well.) =E2=80=94 effectively treating it as a prefix mat= ch =E2=80=94 I used strncmp. Thank you for the reminder=EF=BC=8C Dan. > regards, > dan carpenter >