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Message-ID: <87fsvf65zu.fsf@collabora.com> Date: Wed, 11 Aug 2021 17:12:05 -0400 From: Gabriel Krisman Bertazi <krisman@...labora.com> To: Jan Kara <jack@...e.cz> Cc: jack@...e.com, amir73il@...il.com, djwong@...nel.org, tytso@....edu, david@...morbit.com, dhowells@...hat.com, khazhy@...gle.com, linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org, linux-api@...r.kernel.org, kernel@...labora.com Subject: Re: [PATCH v5 14/23] fanotify: Encode invalid file handler when no inode is provided Jan Kara <jack@...e.cz> writes: > On Wed 04-08-21 12:06:03, Gabriel Krisman Bertazi wrote: >> Instead of failing, encode an invalid file handler in fanotify_encode_fh >> if no inode is provided. This bogus file handler will be reported by >> FAN_FS_ERROR for non-inode errors. >> >> Also adjust the single caller that might rely on failure after passing >> an empty inode. > > It is not 'file handler' but rather 'file handle' - several times in the > changelog and in subject :). > >> Suggested-by: Amir Goldstein <amir73il@...il.com> >> Signed-off-by: Gabriel Krisman Bertazi <krisman@...labora.com> >> --- >> fs/notify/fanotify/fanotify.c | 39 ++++++++++++++++++++--------------- >> fs/notify/fanotify/fanotify.h | 6 ++++-- >> 2 files changed, 26 insertions(+), 19 deletions(-) >> >> diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c >> index 0d6ba218bc01..456c60107d88 100644 >> --- a/fs/notify/fanotify/fanotify.c >> +++ b/fs/notify/fanotify/fanotify.c >> @@ -349,12 +349,6 @@ static int fanotify_encode_fh(struct fanotify_fh *fh, struct inode *inode, >> void *buf = fh->buf; >> int err; >> >> - fh->type = FILEID_ROOT; >> - fh->len = 0; >> - fh->flags = 0; >> - if (!inode) >> - return 0; >> - > > I'd keep the fh->flags initialization here. Otherwise it will not be > initialized on some error returns. > >> @@ -363,8 +357,9 @@ static int fanotify_encode_fh(struct fanotify_fh *fh, struct inode *inode, >> if (fh_len < 4 || WARN_ON_ONCE(fh_len % 4)) >> goto out_err; >> >> - /* No external buffer in a variable size allocated fh */ >> - if (gfp && fh_len > FANOTIFY_INLINE_FH_LEN) { >> + fh->flags = 0; >> + /* No external buffer in a variable size allocated fh or null fh */ >> + if (inode && gfp && fh_len > FANOTIFY_INLINE_FH_LEN) { >> /* Treat failure to allocate fh as failure to encode fh */ >> err = -ENOMEM; >> ext_buf = kmalloc(fh_len, gfp); >> @@ -376,14 +371,24 @@ static int fanotify_encode_fh(struct fanotify_fh *fh, struct inode *inode, >> fh->flags |= FANOTIFY_FH_FLAG_EXT_BUF; >> } >> >> - dwords = fh_len >> 2; >> - type = exportfs_encode_inode_fh(inode, buf, &dwords, NULL); >> - err = -EINVAL; >> - if (!type || type == FILEID_INVALID || fh_len != dwords << 2) >> - goto out_err; >> - >> - fh->type = type; >> - fh->len = fh_len; >> + if (inode) { >> + dwords = fh_len >> 2; >> + type = exportfs_encode_inode_fh(inode, buf, &dwords, NULL); >> + err = -EINVAL; >> + if (!type || type == FILEID_INVALID || fh_len != dwords << 2) >> + goto out_err; >> + fh->type = type; >> + fh->len = fh_len; >> + } else { >> + /* >> + * Invalid FHs are used on FAN_FS_ERROR for errors not >> + * linked to any inode. Caller needs to guarantee the fh >> + * has at least FANOTIFY_NULL_FH_LEN bytes of space. >> + */ >> + fh->type = FILEID_INVALID; >> + fh->len = FANOTIFY_NULL_FH_LEN; >> + memset(buf, 0, FANOTIFY_NULL_FH_LEN); >> + } > > Maybe it will become clearer later during the series but why do you set > fh->len to FANOTIFY_NULL_FH_LEN and not 0? Jan, That is how we encode a NULL file handle (i.e. superblock error). Amir suggested it would be an invalid FILEID_INVALID, with a zeroed handle of size 8. I will improve the comment on the next iteration. -- Gabriel Krisman Bertazi
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