Al Viro <[email protected]> writes: > On Wed, Jun 22, 2022 at 03:45:59PM -0400, Gabriel Krisman Bertazi wrote: > >> +static inline int generic_ci_d_revalidate(struct dentry *dentry, >> + const struct qstr *name, >> + unsigned int flags) >> +{ >> + int is_creation = flags & (LOOKUP_CREATE | LOOKUP_RENAME_TARGET); >> + >> + if (d_is_negative(dentry)) { >> + const struct dentry *parent = READ_ONCE(dentry->d_parent); >> + const struct inode *dir = READ_ONCE(parent->d_inode); >> + >> + if (dir && needs_casefold(dir)) { >> + if (!d_is_casefold_lookup(dentry)) >> + return 0; > > In which conditions does that happen?
Hi Al, This can happen right after a case-sensitive directory is converted to case-insensitive. A previous case-sensitive lookup could have left a negative dentry in the dcache that we need to reject, because it doesn't have the same assurance of absence of all-variation of names as a negative dentry created during a case-insensitive lookup. >> + if (is_creation && >> + (dentry->d_name.len != name->len || >> + memcmp(dentry->d_name.name, name->name, >> name->len))) >> + return 0; >> + } >> + } >> + return 1; >> +} > > Analysis of stability of ->d_name, please. It's *probably* safe, but > the details are subtle and IMO should be accompanied by several asserts. > E.g. "we never get LOOKUP_CREATE in op->intent without O_CREAT in > op->open_flag > for such and such reasons, and we verify that in such and such place"... > > A part of that would be "the call in lookup_dcache() can only get there > with non-zero flags when coming from __lookup_hash(), and that has parent > locked, > stabilizing the name; the same goes for the call in __lookup_slow(), with the > only call chain with possibly non-zero flags is through lookup_slow(), where > we > have the parent locked". However, lookup_fast() and lookup_open() have the > flags come from nd->flags, and LOOKUP_CREATE can be found there in several > areas. > I _think_ we are guaranteed the parent locked in all such call chains, but > that > is definitely worth at least a comment. Thanks for the example of the analysis what you are looking for here. That will help me quite a bit. I wrote this code a while ago and I don't recall the exact details. I will go through the code again and send a new version with the detailed analysis. -- Gabriel Krisman Bertazi _______________________________________________ Linux-f2fs-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
