From: Benjamin Coddington Date: Thu, 11 Jun 2026 21:02:15 +0000 (-0400) Subject: NFSv4: include MAY_WRITE in open permission mask for O_TRUNC X-Git-Tag: v7.2-rc3~21^2~1 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=5140f099ecd8a2f2808b7f7b720ee1bad8468974;p=thirdparty%2Fkernel%2Flinux.git NFSv4: include MAY_WRITE in open permission mask for O_TRUNC POSIX requires write permission to truncate a file, so an open() that specifies O_TRUNC must be authorized for write access regardless of the O_ACCMODE access mode. nfs_open_permission_mask() builds the access mask passed to nfs_may_open(), which is the local authorization gate for OPENs the client serves itself from a cached write delegation via the can_open_delegated() path in nfs4_try_open_cached(). The mask is derived from O_ACCMODE alone, so an open(O_RDONLY | O_TRUNC) against a file the caller cannot write requests only MAY_READ and passes the local check. The OPEN is then satisfied locally and the truncation is issued to the server as a SETATTR(size=0) over the delegation stateid, which the server accepts under standard write-delegation semantics. POSIX requires that this open fail with EACCES. Include MAY_WRITE in the mask whenever O_TRUNC is set so the local check matches the access the server would have enforced. Suggested-by: Trond Myklebust Fixes: af22f94ae02a ("NFSv4: Simplify _nfs4_do_access()") Cc: stable@vger.kernel.org Signed-off-by: Benjamin Coddington Signed-off-by: Anna Schumaker --- diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c index c7b723c18620..c7caffb31935 100644 --- a/fs/nfs/dir.c +++ b/fs/nfs/dir.c @@ -3346,6 +3346,8 @@ static int nfs_open_permission_mask(int openflags) mask |= MAY_READ; if ((openflags & O_ACCMODE) != O_RDONLY) mask |= MAY_WRITE; + if (openflags & O_TRUNC) + mask |= MAY_WRITE; } return mask;